Facebook says an operation likely based in Russia spent $100,000 on divisive adverts during the run up to the US elections.
The social media network said that many of the adverts promoted 470 fake accounts and pages, spreading social and political messages.
Topics included immigration, race and gay rights, although they did not express support for a particular candidate.
The news was announced in a blog post by Facebook’s chief security officer Alex Stamos, who said: “There have been a lot of questions since the 2016 US election about Russian interference in the electoral process.
“One question that has emerged is whether there’s a connection between the Russian efforts and ads purchased on Facebook.
“These are serious claims and we’ve been reviewing a range of activity on our platform to help understand what happened.”
Image: Facebook’s Alex Stamos says the fake accounts have been shut down
Mr Stamos said the ad spending was associated with “roughly 3,000 ads” between June 2015 and May 2017.
Most of the ads were run in 2015 and a quarter of them were targeted at a specific region, he added.
“Our analysis suggests these accounts and pages were affiliated with one another and likely operated out of Russia.
“We don’t allow inauthentic accounts on Facebook, and as a result, we have since shut down the accounts and pages we identified that were still active.”
Alleged Russian interference in the election has been the subject of several investigations in the first months of Donald Trump’s presidency, with US congressional panels also looking into the extent of any tampering.
Moscow has denied any involvement and Mr Trump has denied any collusion by his campaign team, including denouncing the investigations as political witch hunts.
Mr Stamos said that Facebook had also looked for adverts that may have originated in Russia, even those with “very weak signals of a connection and not associated with any known organised effort”.
He said: “This was a broad search, including, for instance, ads bought from accounts with US IP addresses but with the language set to Russian, even though they didn’t necessarily violate any policy or law.
“In this part of our review, we found approximately $50,000 in potentially politically-related ad spending on roughly 2,200 ads.
“We have shared our findings with US authorities investigating these issues, and we will continue to work with them as necessary.”