Russia has intensified its online efforts to derail military funding for Ukraine in the United States and Europe, largely by using harder-to-trace technologies to amplify arguments for isolationism ahead of the U.S. elections, according to disinformation experts and intelligence assessments.

In recent days, intelligence agencies have warned that Russia has found better ways to hide its influence operations, and the Treasury Department issued sanctions last week against two Russian companies that it said supported the Kremlin’s campaign.

The stepped-up operations, run by aides to President Vladimir V. Putin and Russian military intelligence agencies, come at a critical moment in the debate in the United States over support for Ukraine in its war against Russia. While opposition to additional aid may have started without Russian influence, the Kremlin now sees an opportunity.

Russian operatives are laying the groundwork for what could be a stronger push to support candidates who oppose aiding Ukraine, or who call for pulling the United States back from NATO and other alliances, U.S. officials and independent researchers say.

Investigators say that firms working in the “Doppelgänger” network — and Russian intelligence agencies duplicating the tactics — are using the techniques to replicate and distort legitimate news sites in order to undermine continued aid to Ukraine.

These techniques are subtle and far more skillful than what Russia attempted in 2016, when it made up Facebook posts or tweets in the names of nonexistent Americans, and used them to fuel protests over immigration or other hot-button issues.

The loosely linked “Doppelgänger” creates fake versions of real news websites in the United States, Israel, Germany and Japan, among other countries. It often promotes websites previously associated with Russia’s military intelligence agency, known as the G.R.U.

The result is that much of the original speech is First Amendment-protected — say a member of Congress declaring that resources being sent to Ukraine should instead be used to patrol the southern border of the United States. But the amplification is engineered in Russia or by Russian influencers.

Mr. Putin has given responsibility for a growing number of influence operations to a key lieutenant, Sergei Kiriyenko, according to American and European officials. The Treasury Department last Wednesday imposed sanctions on people associated with Mr. Kiriyenko’s operations.

Researchers at Alethea, an anti-disinformation company, have identified a group affiliated with the G.R.U. that is using hard-to-detect techniques to spread similar messages on social media. A report by Alethea echoed a recent assessment by American intelligence agencies that said Russia would continue to “better hide their hand” while conducting influence operations.

“The network demonstrates an evolution of Russian objectives with their information operations,” Lisa Kaplan, the firm’s founder and chief executive, said in an interview. “Where the Russians previously sought to sow chaos, now they appear to be singularly focused on influencing democracies to elect candidates that do not support sending aid to Ukraine — which in turn supports isolationist, protectionist candidates and policies.”

“This long-term strategy, if effective, would result in reduced support for Ukraine globally,” she said.

American officials note, however, that these techniques make identifying — and calling out — Russian operations particularly difficult.

In the 2016 election, the Internet Research Agency, a Russian troll farm that waged information warfare against the United States, spewed out thousands of social media posts, pretending they were from Americans. By the 2020 election, the National Security Agency learned how to disrupt the operations inside Russia.

Moscow moved to shut down the Internet Research Agency after its founder, Yevgeny V. Prigozhin, staged a short-lived mutiny against the Russian military last year. People affiliated with the group remain active. But U.S. officials and experts say it is no longer the main Russian influence effort.

“The Internet Research Agency in many ways was just a place holder for what became a much more expansive information effort in traditional media and social media,” said Clint Watts, the general manager of Microsoft’s Threat Analysis Center.

The latest efforts are more directly controlled by the Kremlin. Before the Treasury sanctions last week, the State Department outlined what it said were efforts by the two Russian companies, the Social Design Agency, a public relations company, and Structura National Technologies, an information technology firm, to create disinformation campaigns.

American intelligence agencies do not believe the Kremlin has begun its full-bore influence effort. Mr. Putin will probably shift at some point from the anti-Ukraine messaging to influence operations that more directly support the candidacy of former President Donald J. Trump, the presumptive Republican nominee.

Mr. Putin is not likely to order a major effort in the presidential election until after the party conventions this summer, officials and experts said.

“What we’ve observed is the Russians, and a number of other adversarial countries, thinking about how and when they might influence the election,” said Jim Himes, Democrat of Connecticut and a senior member of the House Intelligence Committee.

Mr. Putin argues that the United States has sought to influence Russian politics, including the presidential election this month, in which he was, unsurprisingly, re-elected by an overwhelming margin. It is not clear how much Mr. Putin regards U.S. sanctions issued after the death of the opposition leader Aleksei A. Navalny as a kind of interference in his politics.

“Putin believes in his heart that we meddle in his elections,” Mr. Himes said. “Things like contact with dissident groups or amplifying Navalny’s message. Putin sees all of that as interference on the part of the U.S. He regards things like senators and congressmen criticizing his election as election interference.”

The Russian activity captivating American attention is not limited to influence operations. Russia’s S.V.R., the intelligence agency that was most active in the 2016 election and that was behind the “SolarWinds” hack that gained entry to scores of government agencies and major American companies, has been in a monthslong attack on Microsoft. The effort appears aimed at gaining access to emails and corporate data.

And U.S. officials say that ransomware attacks continue to surge from Russian territory.

A wave of such attacks prompted President Biden and Mr. Putin’s only leader-to-leader summit, in 2021. An effort to work together on stemming those attacks collapsed as Russia’s invasion of Ukraine began the next year. Today, the hacking campaigns reap millions of dollars for criminal groups, while often serving the Kremlin’s agenda of disrupting American health care, government services and utilities.

In their annual threat assessment, the intelligence agencies said that Russia was trying to sow discord among voters in the United States and its allies around the world, and that the war in Ukraine “will continue to feature heavily in its messaging.”

“Moscow views U.S. elections as opportunities and has conducted influence operations for decades,” the intelligence report said. “Russia is contemplating how U.S. electoral outcomes in 2024 could impact Western support to Ukraine and probably will attempt to affect the elections in ways that best support its interests and goals.”

Russia is likely to be the most active foreign power seeking to influence the presidential election, though China and Iran have also stepped up their efforts, Mr. Himes said.

“It’s important to remember that the nature of election meddling is very different when you’re talking about the Russians,” Mr. Himes said. “The Russians are orders of magnitude more intense and more focused on what we’ve seen from the Chinese, Iranians and others.”

After the 2016 vote, Democrats and Republicans fiercely debated whether Mr. Putin simply wanted to create chaos in the American electorate or actively supported Mr. Trump. The intelligence agencies concluded in that election, and in 2020, that Russia sought to bolster Mr. Trump.

Intelligence agencies believe the Russian government again favors Mr. Trump’s election, largely because of his skepticism about aid to Ukraine. But how explicitly Russian influence operations will support Mr. Trump or denigrate Mr. Biden is unknown, according to American officials.

The attack at a concert hall just outside Moscow that killed 139 people last Friday has prompted some Russians to call for bringing back capital punishment in Russia, and to execute the assailants.

Through a combination of presidential action and court rulings, Russia has had a moratorium on the death penalty for 28 years. And yet capital punishment remains on the books — suspended but not abolished outright.

Russian officials disagree on whether and how it could be resurrected, and the country’s Constitutional Court said on Tuesday that it would look into the matter.

Here is a look at where the issue stands.

Who is advocating or opposing the death penalty?

A number of public figures have demanded execution of the concert hall attackers, described by officials as militant Islamists from Tajikistan, in Central Asia. Such calls have surfaced periodically, particularly after terrorist attacks, but it is not clear how widespread support for them is, and they have prominent opponents, too.

On Monday, Dmitri A. Medvedev, a former president and prime minister of Russia, wrote on Telegram: “Is it necessary to kill them? Necessary. And it will be done.”

He added that everyone who was involved in the attacks, including those who funded and supported them, should be killed.

But Lidia Mikheeva, the secretary of the Civic Chamber, a government advisory group, told the state news agency Tass that ending the death penalty was one of the most important accomplishments in modern Russian history. “If we don’t want to roll back to a time of savagery and barbarism, then we should all stop and think,” she said.

Where does Putin stand?

Nothing is likely to change without the say-so of Vladimir V. Putin, the autocratic president who largely controls the Parliament. He has publicly, repeatedly opposed the death penalty in years past.

Mr. Putin and his security apparatus have often been accused of killing or trying to kill his enemies, at home or abroad — journalists, political opponents, business leaders, former spies and others. The opposition leader Aleksei A. Navalny, who survived an assassination attempt with a nerve agent, died last month in a Russian prison system that his allies said had mistreated him and denied him medical care.

And yet in 2002, Mr. Putin said, “as long as it’s up to me, there will be no death penalty in Russia,” though he said reinstating it would be popular. In 2007, he said at a conference that formal capital punishment was “senseless and counterproductive,” according to Russian media reports. In 2022, he said his position “has not changed.”

As for the debate after the concert hall massacre, “We are not currently taking part in this discussion,” said Dmitri S. Peskov, the Kremlin spokesman, according to Tass.

How did the moratorium start, and how has it continued?

The Soviet Union was one of the world’s most frequent users of capital punishment, and after the country broke up, Russia continued to carry out executions.

But in 1996, to win admission to the Council of Europe, a human rights group, President Boris N. Yeltsin, Mr. Putin’s predecessor, agreed to place a moratorium on the death penalty and to completely abolish it within three years.

Russia’s Parliament did not go along with the plan. It did not ratify the European Convention on Human Rights, which Mr. Yeltsin’s government had signed, and it adopted a new criminal code that kept capital punishment as an option.

In 1999, the Constitutional Court stepped in, ruling that until jury trials were in place across Russia, the death penalty could not be used. In 2009, after jury trials had been instituted, the court ruled the moratorium would remain in effect, abiding by the Council of Europe’s rules, in part because more than a decade without capital punishment had given people an expectation that it would not be used.

“Stable guarantees of the human right not to be subjected to the death penalty have been formed and a constitutional and legal regime has emerged,” the court wrote.

What would be required to resume executions?

That is unclear.

After Russia invaded Ukraine in 2022, the Council of Europe expelled Russia, meaning Moscow was no longer considered a party to its human rights convention — the original basis for the moratorium.

At the time, Valeriy D. Zorkin, the head of the Constitutional Court, said that bringing back the death penalty back would be impossible without adopting a new Constitution.

“Despite the current extraordinary situation, I think it would be a big mistake to turn away from the path of humanization of legislative policy that we have generally followed in recent decades,” he said in a lecture at the St. Petersburg International Legal Forum. “And, in particular, a rejection of the moratorium on the death penalty in Russia, which some politicians are already calling for, would now be a very bad signal to society.”

But some politicians insisted that without the human rights convention as a barrier, capital punishment could be reinstated without any constitutional change.

That position voiced this week by Vyacheslav V. Volodin, speaker of the Duma, the lower house of Russia’s Parliament. The Constitutional Court, he said, could lift the moratorium.

“Me and you all, we left the Council of Europe, right? Right,” he said.

At a memorial service this week outside the concert hall where Islamist extremists are suspected of carrying out a deadly terrorist attack, one of Russia’s most popular pro-Kremlin rappers warned “right-wing and far-right groups” that they must not “incite ethnic hatred.”

At a televised meeting about the attack, Russia’s top prosecutor, Igor Krasnov, pledged that his service was paying “special attention” to preventing “interethnic and interfaith conflicts.”

And when President Vladimir V. Putin made his first comments on the tragedy last weekend, he said he would not allow anyone to “sow the poisonous seeds of hatred, panic and discord in our multiethnic society.”

In the wake of the assault near Moscow that killed 139 people last Friday, there has been a recurring theme in the Kremlin’s response: a fear that the tragedy could spur ethnic strife inside Russia. While Mr. Putin and his security chiefs are accusing Ukraine — without evidence — of having helped organize the killing, the fact that the four detained suspects in the attack are from the predominantly Muslim Central Asian country of Tajikistan is stoking anti-migrant rhetoric online.

For Mr. Putin, the problem is magnified by the competing priorities of his war in Ukraine. Members of Muslim minority groups make up a significant share of the Russian soldiers fighting and dying. Migrants from Central Asia are providing much of the labor that keeps Russia’s economy running and its military supply chain humming.

But many of the most fervent supporters of Mr. Putin’s invasion are Russian nationalists whose popular, pro-war blogs on the Telegram messaging app have brimmed with xenophobia in the days since the attack.

“The borders have to be shut down as much as possible, if not closed,” said one. “The situation now has shown that Russian society is on the brink.”

As a result, the Kremlin is walking a fine line, trying to keep war supporters happy by promising tougher action against migrants while trying to prevent tensions from flaring across society. The potential for violence was highlighted in October, when an antisemitic mob stormed an airport in the predominantly Muslim Russian region of Dagestan to confront a passenger plane arriving from Israel.

“The authorities see this as a very big, serious threat,” Sergey Markov, a pro-Putin political analyst in Moscow and a former Kremlin adviser, said in a phone interview. “That’s why all efforts are being made now to calm down public opinion.”

Caught in the middle are millions of migrant workers and ethnic-minority Russians who are already facing an increase on city streets in the kind of racial profiling that was commonplace even before the attack. Svetlana Gannushkina, a longtime Russian human rights defender, said on Tuesday that she was scrambling to try to help a Tajik man who had just been detained because the police “are looking for Tajiks” and “saw a person with such an appearance.”

“They need migrants as cannon fodder” for the Russian Army “and as labor,” Ms. Gannushkina said in a phone interview from Moscow. “And when they need to fulfill the plan on fighting terrorism, they’ll also focus on this group” of Tajiks, she said.

Nearly a million citizens of Tajikistan, which has a population of about 10 million, were registered in Russia as migrant workers last year, according to government statistics. They are among the millions of migrant laborers in Russia from across the former Soviet republics of Central Asia, a driving force in Russia’s economy, from food delivery and construction to factory work.

A manager of a food business in Moscow that employs Tajiks said in an interview that the mood in the Russian capital reminded her of the 2000s, when Muslims from the Caucasus region faced widespread discrimination in the wake of terrorist attacks and the wars in Chechnya. Tajiks in Moscow are so apprehensive they are hardly going outside at all, she said, requesting anonymity because she feared repercussions for speaking to a Western journalist.

“There’s already no supply of labor because of the S.V.O.,” she added, using the common Russian abbreviation for the Kremlin’s “special military operation” against Ukraine. “And now it’ll be even worse.”

Ethnic tensions have been an enduring challenge for Mr. Putin during his almost quarter-century rule, but he has also tried to use them to his geopolitical advantage. Mr. Putin’s rise to power was shaped by war in the southern, predominantly Muslim region of Chechnya, where Russia sought to brutally extinguish separatist and extremist movements. He has also helped foment separatism in places like the Georgian regions of South Ossetia and Abkhazia, taking sides in long-simmering conflicts there to expand Russia’s influence.

Mr. Putin’s government is already trying to show the public that it stands ready to take action against migrants. A top lawmaker proposed on Tuesday that firearms sales be banned to newly naturalized Russian citizens. Mr. Krasnov, the top prosecutor, said that the number of crimes carried out by migrants rose by 75 percent in 2023, without providing specific details. “We need to develop balanced solutions based on the need to ensure the safety of citizens and the economic expediency of using foreign labor,” he added.

Far from trying to keep foreigners out, Russia has made it easier for migrants to become Russian citizens since the start of its full-scale invasion of Ukraine in February 2022. A primary reason appears to be the military’s need for soldiers in Ukraine, and police raids targeting migrant workers to compel them to register for military service have become commonplace in Russian news reports.

As a result, Tajik migrants in Moscow now fear not only deportation, but also the possibility that they could be pressed into service in Ukraine, said Saidanvar, 25, a Tajik human rights activist who recently left Moscow. He asked that his last name not be used for security reasons.

“Tajiks are really afraid,” he said in an interview, “that the Russian authorities will start sending Tajiks to the front en masse to fight as a sort of revenge against our Tajik people.”

In his speeches on the war, Mr. Putin has paid frequent lip service to Russia as a multiethnic state — a legacy of the Russian and Soviet empires. In March 2022, after describing the heroism of a soldier from Dagestan, Mr. Putin enumerated some of Russia’s ethnic groups by saying: “I am a Lak, I am a Dagestani, I am a Chechen, an Ingush, a Russian, a Tatar, a Jew, a Mordvin, an Ossetian.”

In his rhetoric about his conflict with the West, Mr. Putin has frequently accused Russia’s adversaries of trying to stir up ethnic strife in Russia. That was his response to the Dagestan airport riot in October, which he baselessly blamed on Western intelligence agencies and Ukraine. That is also increasingly at the center of his response to Friday’s terrorist attack, which the Islamic State claimed responsibility for and American officials say was carried out by a branch of the extremist group. On Tuesday, the head of Russia’s domestic intelligence agency claimed that Ukrainian, British and American spies might have been behind it.

The upshot appears to be that the Kremlin is seeking to refocus anger over the attack toward Ukraine while trying to show the public that it is taking concerns about migration into account.

“They’re going to grab the Tajiks and blame the Ukrainians,” Ms. Gannushkina, the human rights defender, said. “It was clear from the very beginning.”

Still, Mr. Markov, the pro-Kremlin analyst, said he saw tensions over migration policy even inside Mr. Putin’s powerful security establishment. Anti-immigrant law enforcement and intelligence officials, he said, were at odds with a military-industrial complex that needs migrant labor.

“It’s a contradiction,” he said. “And this terror attack has sharply aggravated this problem.”