The ads focused on "amplifying divisive social and political messages across the ideological spectrum" and used techniques Facebook previously identified as those used by disinformation campaigns, Stamos said.
It said it had discovered that the $100,000 had been used to buy roughly 3,000 ads connected to 470 accounts all "likely" associated with each other and operated out of Russian Federation. The ads often mentioned particular political issues, such as LGBT rights or gun control, but rarely mentioned a specific political candidate or the United States presidential election.
Facebook's concession that it sold $100,000 in ads to Russian-linked accounts previous year may be "just the tip of the iceberg" of how social networks were used to interfere in the election, warned the top Democrat on the Senate Intelligence Committee. About 3,000 ads were purchased for $100,000 and around one-quarter of the ads employed geographical targeting when they ran from June 2015 to May 2017.
Facebook's findings come as U.S. investigators probe alleged Russian interference in the USA election, which was eventually won by Republican Donald Trump.
Huge tech platforms like Facebook and Google increasingly control the flow and dissemination of news and information around the world, and revelations like this give cause for more skepticism about the source and quality of news on social media.
Top Russian officials, including President Vladimir Putin, have repeatedly rejected accusations the country meddled in the USA election.
The ads were traced to a Russian "troll farm", a Facebook official said on the condition of anonymity because he is not authorized to speak publicly on the matter.
Mark Warner, the top Democrat on a Senate committee looking into the interference, said he wants to talk with Facebook about how Russian agents may have used the platform to spread false stories.
Facebook has targeted Russia in a review of ad purchases, searching for those which originated in Russia or used the Russian language from an IP address in the U.S. - even though the ads "didn't necessarily violate any policy or law". In hunting for other suspect ads, Facebook turned up $50,000 spent on 2,200 ads it says could have been politically related.
Facebook made its statement on Wednesday, blaming an operation likely based in Russian Federation for deliberately spearheading divisive political and social messages.
In the review presented to Congressional investigators, Facebook said it had found an additional $50,000 in political ad spending during the election from other accounts connected to Russian Federation. Both committees are hunting for evidence of alleged Russian meddling in the 2016 election, including potential collusion between Moscow and Donald Trump's campaign.
"We know they had a cyber operation, we suspect USA persons may have been involved, now we know a USA company was used".