Facebook says it has identified a new co-ordinated political influence campaign to mislead its users and sow dissension among voters ahead of November's US congressional elections.
It said it had removed 32 pages and accounts from Facebook and Instagram, part of an effort to combat foreign meddling in US elections.
The company stopped short of identifying the source, but members of Congress who have been briefed by Facebook on the matter say the methodology of the influence campaign suggested Russian involvement.
"I can say I think with pretty high confidence I think this is Russian-related," Senator Mark Warner, the top Democrat on the Senate Intelligence Committee, said.
A Russian propaganda arm tried to tamper in the 2016 US election by posting and buying ads on Facebook, according to the company and US intelligence agencies.
In February, the US Justice Department indicted 13 Russian nationals, and the St. Petersburg-based Internet Research Agency, for interfering.
Moscow has denied involvement.
Sheryl Sandberg, Facebook's chief operating officer, said the attempts to manipulate public opinion would likely become more sophisticated to evade Facebook's scrutiny, calling it an "arms race."
The White House said the administration was supportive of Facebook's actions.
"We applaud efforts by our private-sector partners to combat an array of threats that occur in cyberspace, including malign influence," said Garrett Marquis, a spokesman for the National Security Council.
President Donald Trump has come under fire for discounting the threat of interference in the congressional elections.
During his summit with Russian President Vladimir Putin in Helsinki earlier this month, Trump appeared to state that he believed Russia was no longer trying to influence the US election process.
Trump later amended that, saying he was "very concerned" about Russian interference in the election.
Facebook has identified influence activity around at least two issues, including a counter-protest to the Unite the Right 2 rally set next week in Washington.
A previous event last year in Charlottesville, Virginia, led to violence by white supremacists.
"This kind of behaviour is not allowed on Facebook because we don't want people or organisations creating networks of accounts to mislead others about who they are, or what they're doing," the company said.
More than 290,000 accounts followed at least one of the pages and about $11,000 had been spent on about 150 ads, Facebook said. The pages had created about 30 events since May 2017.
