Russia's government didn't just hack and leak documents from U.S. political groups during the presidential campaign: It used social media as a weapon to influence perceptions about the election, according to cybersecurity company FireEye Inc.

Material stolen by Russia's intelligence services was feverishly promoted by online personas and numerous fake accounts through links to leaked material and misleading narratives, according to an analysis of thousands of postings, links and documents by FireEye, which tracks Russian and Chinese hackers breaking into U.S. systems. The operation was a new and belligerent escalation by Moscow in the cyber domain, company Chairman David DeWalt said.

"The dawning of Russia as a cyber power is at a whole other level than it ever was before," DeWalt said in an interview in Washington. "We've seen what I believe is the most historical event maybe in American democracy history in terms of the Russian campaign."

The closeness of the Nov. 8 election sparked scrutiny over the spread of fake news and has fueled demands from Green Party candidate Jill Stein, backed by some Democrats and independents, for a recount in key states lost by Democrat Hillary Clinton. President-elect Donald Trump responded on Twitter that "millions" of people voted illegally, which he said may have been what cost him the popular vote, but he offered no evidence.

A computer scientist for Stein said security flaws in voting machines and suspicions of Russian meddling justified the recount efforts. J. Alex Halderman, a professor at the University of Michigan, said hackers could have infected Pennsylvania's voting machines with malware designed to lay dormant for weeks, pop up on Election Day and then erase itself without a trace. Trump narrowly won Pennsylvania as well as two other states where Stein's campaign may seek recounts, Michigan and Wisconsin.

Kevin Mandia, chief executive officer, of Milpitas, California-based FireEye, and DeWalt said in the interview this week that they haven't seen any evidence that U.S. vote tabulation systems were hacked. And U.S. officials have said they saw only "minor" cyber incidents on Election Day.

"We did not see anything that I would characterize as significant," Homeland Security Secretary Jeh Johnson said at a Bloomberg Government event Nov. 14 in Washington. "There were minor incidents here and there of the type that you would normally expect, but nothing significant."

Russian officials have repeatedly rejected accusations that the government hacks or supports groups that does so on its behalf.

That hasn't quelled concerns. The activity detected in the FireEye analysis echoed the Russian strategy of information warfare seen previously in cyber attacks on Estonia, Georgia and Ukraine, where a simmering border conflict has claimed almost 10,000 lives over 2 1/2 years.

The strategy isn't limited to online media. The U.K. in October closed the British bank account for RT, a Russian state-controlled news service that was reprimanded by the U.K. media regulator Ofcom for biased or misleading reporting on Syria and Ukraine. Russia protested the move, saying it was being targeted for political reasons.

On Tuesday, Democrats on the Senate Intelligence Committee sent President Barack Obama a letter asking him to declassify information about Russian activity related to the U.S. election.

"We believe there is additional information concerning the Russian government and the U.S. election that should be declassified and released to the public," the senators wrote. "We are conveying specifics through classified channels."

A month before the election, the Office of the Director of National Intelligence and the Homeland Security Department issued a joint statement saying American intelligence agencies were confident that Russia directed hacking against U.S. political groups.

"The recent disclosures of alleged hacked e-mails on sites like DCLeaks.com and WikiLeaks and by the Guccifer 2.0 online persona are consistent with the methods and motivations of Russian-directed efforts," according to the statement. "The Russians have used similar tactics and techniques across Europe and Eurasia, for example, to influence public opinion there. We believe, based on the scope and sensitivity of these efforts, that only Russia's senior-most officials could have authorized these activities."

In line with those findings, FireEye has mapped what it says is a Russian-backed campaign using at least six key false hacktivist personas to advance the country's interests, including Guccifer 2.0, DC Leaks, Anonymous Poland and Fancy Bears' Hack Team. The company's autopsy also includes thousands of postings on Twitter as well as fake social-media accounts used to pass the information back and forth to generate an online buzz.

The hacking extends to trying to use legitimate websites to promote stolen material. Guccifer 2.0, for example, first promoted stolen documents from the Democratic National Committee through The Smoking Gun and Gawker. There's no evidence that those websites knew that hacked material given to them was part of a broad campaign to meddle in the U.S. election.

The campaign also includes what FireEye terms "direct advocacy," in which the personas direct tweets promoting stolen or false information at the accounts of influential people such as journalists, and "indirect advocacy"in which social-media accounts seemingly unaffiliated with the personas also engage in promotion.

Even after the U.S. election, there are few signs that Russia's actions are abating, creating a complicated, emerging challenge for the incoming Trump administration, FireEye's DeWalt said. During the campaign, Trump was deferential to Russia and its president, Vladimir Putin, and repeatedly questioned the conclusion of the U.S. intelligence community that Russia was meddling in American elections.

For years, Russian spies carried out stealthy hacking attacks aimed at hiding their identities, said Mandia, the FireEye CEO. Their tactics began to change around the fall of 2014 and have now escalated to include leaking stolen documents and apparently caring less about operational security or getting caught, Mandia said.

"That's a change in the rules of engagement," Mandia said. "All of a sudden, they're more of a tank through the cornfield when they hack, not a whisper or a ghost."