Thousands of Russian-made Facebook adverts targeting US voters have been released online.
The House Intelligence Committee Democrats published more than 3500 of the adverts, bought by the Internet Research Agency (IRA).
Many of the adverts were designed to sow discord ahead of the 2016 presidential election, reputedly to sway it in favour of the divisive Republican candidate, Donald Trump.
"Russia sought to weaponise social media to drive a wedge between Americans, and in an attempt to sway the 2016 election," tweeted Adam Schiff, the Democrats' ranking member on the House Intelligence Committee.
"They created fake accounts, pages and communities to push divisive online content and videos, and to mobilise real Americans."
Facebook responded by saying it was "too slow to spot this type of information operations interference", and has made changes since.
"This will never be a solved problem because we're up against determined, creative and well-funded adversaries," the company said in a statement. "But we are making steady progress."
The ads reached millions of American voters, and pushed readers towards more than 400 fake activist pages, including 'Blacktivist', 'Being Patriotic', 'LGBT United', 'Heart of Texas', 'Secured Borders' and 'Back the Badge'.
Congress released not just the ads themselves, but how much was spent on them and how many clicks they got.
The Washington Post noted that none of the most popular ads and groups specifically mentioned Mr Trump or his opponent Hillary Clinton.
"Instead, they're broadly political, meant, it seems, to encourage association with divisive issues in US politics," wrote Philip Bump.
"In April, we removed 70 Facebook and 65 Instagram accounts - as well as 138 Facebook Pages - controlled by the IRA," said Facebook.
"The IRA has repeatedly used complex networks of inauthentic accounts to deceive and manipulate people in the US, Europe and Russia - and we don't want them on Facebook anywhere in the world."
Mr Schiff said Facebook is working closely with the authorities in their investigation into the extent of the Russian interference on social media.
"The only way we can begin to inoculate ourselves against a future attack is to see first-hand the types of messages, themes and imagery the Russians used to divide us."
Facebook says from now on, political ad buyers will have to verify who they are, and this will be publicly accessible by users of the site. Administrators of popular pages may also be asked to verify their identity.