Facebook said roughly 10 million people saw advertisements bought by Russian groups trying to influence the 2016 U.S. election, the first time the company has shared the reach and potential impact of such ads.
Facebook also said it's "possible" that there are more such ads that it hasn't yet found.
The company released the details on some 3,000 ads the same day they sent them to Congressional committee members in the House and Senate, who are looking at how Russian agents tried to sway last year's Presidential election.
Some of the ads were paid for in Russian currency, Facebook said in a statement.
The company has been asked to appear at public hearings by three different committees in coming weeks to give details on the Russian ad campaign, which highlighted hot-button, divisive issues such as race to try and sway voters.
Facebook admitted in its statement there are limits to its ability to stop people from using its site to undermine democracy.
"Even when we have taken all steps to control abuse, there will be political and social content that will appear on our platform that people will find objectionable, and that we will find objectionable. We permit these messages because we share the values of free speech," the company's statement said.
Facebook has faced mounting criticism in Washington about its response to the propaganda and misinformation Russia-based organizations placed on its site.
Senator Mark Warner, the ranking Democrat on the Senate Intelligence Committee, has said he intends to introduce a bill that will remove an exemption for online political ads that have previously shielded their buyers from public scrutiny.
CEO Mark Zuckerberg late last year had said it was "crazy" to think that the site he founded was used that way.
On Sept. 21, however, Zuckerberg apologized for that comment and said the company was committed to stopping foreign governments from influencing U.S. elections.
"Now, I wish I could tell you we're going to be able to stop all interference, but that wouldn't be realistic. There will always be bad people in the world, and we can't prevent all governments from all interference. But we can make it harder. We can make it a lot harder. And that's what we're going to do," Zuckerberg said in his post last month.