Facebook has handed over to congressional committees more than 3,000 ads purchased during the 2016 election campaign by a firm with ties to Russian intelligence.
Facebook has refused to make the ads public, citing privacy concerns.
The use of social media was part of a broad effort by the Kremlin to help then-Republican nominee Donald Trump and harm Democratic nominee Hillary Clinton, U.S. intelligence agencies said in a January report.
In most cases, the social media ads did not refer to particular candidates.
They focused instead on divisive themes such as race, gay rights, gun control and immigration.
Facebook disclosed the existence of the ads last month. It said they were purchased through 470 fake accounts traced back to the Internet Research Agency, a Russian entity known for posting pro-Kremlin propaganda online.