The companies said the F.B.I. had warned them that a so-called troll farm in St. Petersburg set up a network of fake user accounts and a website.
Facebook and Twitter said on Tuesday that they had taken down a Russian disinformation campaign The Russian group that interfered in the 2016 presidential election is at it again, using a network of fake accounts and a website set up to look like a left-wing news site, Facebook and Twitter said on Tuesday.
The disinformation campaign by the Kremlin-backed group, known as the Internet Research Agency, is the first public evidence that the agency is trying to repeat its efforts from four years ago and push voters away from the Democratic presidential candidate, Joseph R. Biden Jr., to help President Trump.
Intelligence agencies have warned for months that Russia and other countries were actively trying to disrupt the November election, and that Russian intelligence agencies were feeding conspiracy theories designed to alienate Americans by laundering them through fringe sites and social media.
Now Facebook and Twitter are offering evidence of this meddling, even as the White House in recent weeks has sought to more tightly control the flow of information about foreign threats to November’s election and downplay Russian interference. The Trump administration’s top intelligence official as recently as Sunday has tried to suggest that China is a graver risk than Moscow.
Some American officials are worried about a broad effort by Russian intelligence to use fringe websites, spread conspiracy theories and sow division in the United States. And some of the activity Facebook and Twitter identified Tuesday was just that kind of information laundering.
The fake network and site did not reach as big an audience as the group’s efforts in 2016, but the campaign came with a new wrinkle: The Russians hired real Americans to write for the website. The site, called Peace Data, also used personas with computer-generated images to create what looked like a legitimate news organization.
The Internet Research Agency was very active in the 2016 presidential election, and a recent bipartisan senate intelligence committee report detailed Russian interference in support of Mr. Trump’s election.
The group has been a less important part of Russia’s operations this year, according to two American intelligence officials, who spoke on the condition of anonymity. The group’s recently discovered activities on Twitter and Facebook were almost overt, designed to be detected, the officials said.
But the Peace Data site appeared to be a more worrying example of “information laundering” a more covert and potentially dangerous effort by Moscow. Russian intelligence agencies have used allies and operatives to place articles, including disinformation, into various fringe websites.
“The Russians are trying harder to hide; they are increasingly putting up more and more layers of obfuscation,” said Ben Nimmo, whose firm, Graphika, worked with Facebook to release a report on the fake site. “But they are still getting caught.”
The I.R.A. advertised for writers on an online job board, according to one American freelancer who wrote for Peace Data.
The writer asked to remain anonymous because he did not want his professional career affected by his unknowing cooperation in a Russian operation. He said he answered the job ad with some links to his recent work, and received an email response immediately asking him to submit new articles on any theme of his choosing.
In his earlier work, the writer had frequently challenged whether Mr. Biden represented the progressive values of the Democratic Party and whether he deserved the vote of left-wing Americans.
He said his articles for the website were barely edited. He was happy, he added, to be receiving payment for his work, even though his new bosses were offering him only $75 per story. The money, he added, was sent through an electronic payment.