Russia-based operatives published around 80,000 posts on Facebook over a two year period in an effort to sway US politics, the social media network said.
It estimates around 126million Americans may have seen the posts during that time.
Facebook’s latest data on the Russia-linked posts - possibly reaching around half of the US population of voting age - far exceeds the company’s previous disclosures.
Twitter separately has found 2,752 accounts linked to Russian operatives, a source familiar with the company’s written testimony said. That estimate is up from a tally of 201 accounts that Twitter reported in September.
Google, owned by Alphabet Inc, said in a statement on Monday it had found $4,700 in Russia-linked ad spending during the 2016 US election cycle, and that it would build a database of election ads.
Executives from Facebook, Twitter and Google are scheduled to appear before three congressional committees this week on alleged Russian attempts to spread misinformation in the months before and after the 2016 US presidential election.
The Russian government has denied any attempts to sway the election, in which President Donald Trump, a Republican, defeated Democrat Hillary Clinton.
Facebook’s lawyer Colin Stretch said in the written testimony that the 80,000 posts from Russia’s Internet Research Agency were a tiny fraction of content on Facebook, equal to one out of 23,000 posts.
However, the posts violated Facebook’s terms of service, and any amount of such activity using fake accounts is too much, Stretch said.
“These actions run counter to Facebook’s mission of building community and everything we stand for. And we are determined to do everything we can to address this new threat,” he wrote.
The 80,000 posts were published between June 2015 and August 2017. Most of them focused on divisive social and political messages such as race relations, Facebook said.
Twitter’s revised estimate of how many Russia-linked accounts were on its service comes a month after an influential Democratic senator, Mark Warner, slammed it for what he called an insufficient investigation.
Twitter has suspended all 2,752 accounts that it tracked to Russia’s Internet Research Agency, and it has given US congressional investigators the account names.
“State-sanctioned manipulation of elections by sophisticated foreign actors is a new challenge for us - and one that we are determined to meet,” Twitter said in written testimony.