Facebook says an estimated 10 million people in the U.S. saw at least one of the 3,000 political ads it says were bought by accounts linked to the Russian government.
The figure, disclosed by Facebook for the first time on Monday, underscores how effective Russian meddling on social media could be with even a minimal investment.
The ad buyers spent just $100,000 over two years to target 10 million people, according to figures Facebook has provided about the ad buys. That's an audience roughly equivalent to the population of Michigan.
More than half of the ads were seen after the 2016 presidential election, indicating that Russian efforts went well beyond meddling during the campaign and may continue to this day.
"Forty-four percent of the ads were seen before the U.S. election on Nov. 8, 2016, fifty-six percent were seen after the election," Elliot Schrage, Facebook's vice president for policy and communications, said in a new post on Monday.
Schrage acknowledged it was "possible" that there were more Russian-bought political ads on the network that Facebook has yet to identify.
"We're still looking for abuse and bad actors on our platform — our internal investigation continues," Schrage wrote. "We hope that by cooperating with Congress, the Special Counsel and our industry partners, we will help keep bad actors off our platform."
Facebook's disclosure came just hours after it gave congress detailed record of the ads, including data about the buyers and their targeting efforts. Those records were given to the Senate and House Intelligence and Judiciary Committees.
In his post, Schrage wrote that most of the ads "appear to focus on divisive social and political messages across the ideological spectrum, touching on topics from LGBT matters to race issues to immigration to gun rights."
That description matches what CNN has already reported about the apparent goal of the Russian buyers: to amplify political discord in the United States and fuel an atmosphere of divisiveness and chaos, especially during the presidential election.
Schrage's post also addressed a number of questions about how Facebook had identified the ads and what it was doing to stop foreign nationals from meddling in American politics.
But Schrage also made clear that the Russians' use of Facebook represented a small piece of "a much larger puzzle," and that Congress and Special Counsel Robert Mueller were best-suited to address questions about foreign meddling going forward.
"The 2016 US election was the first where evidence has been widely reported that foreign actors sought to exploit the internet to influence voter behavior," Schrage wrote. "We understand more about how our service was abused and we will continue to investigate to learn all we can. We know that our experience is only a small piece of a much larger puzzle. Congress and the Special Counsel are best placed to put these pieces together because they have much broader investigative power to obtain information from other sources."
Facebook's decision to give the ads to Congress means the pressure is now on lawmakers to release the ads to the public.
Representative Adam Schiff, the top Democratic on the House Intelligence Committee, said Monday that he hoped to release "a representative sampling of these ads" next month, following the public hearing with Facebook and other tech companies.
Schiff also said he was "committed to making all of these ads public as soon as possible, working closely with Facebook to address any privacy considerations."
But Republican Senator Richard Burr, who heads the Senate Intelligence Committee, said release of the documents "won't happen out of the Senate Intelligence Committee"
"We don't release documents," Burr told CNN on Monday. "It's a bad precedent to set for anybody else that would produce documents."
Asked about Facebook giving Congress permission to release the ads, Burr said, "If they give us permission then they should release it themselves."
Facebook has already handed copies of the ads and information about the relevant accounts over to Special Counsel Robert Mueller, who is conducting an investigation into Russian meddling in the 2016 election.
The Senate Intelligence Committee has also called on representatives from Facebook, Twitter and Alphabet, the Google parent company, to testify in a public hearing on November 1. None of the companies has said if it will attend the hearing.