Facebook will hand over contents of 3,000 adverts to congressional investigators looking at claims of interference in the US presidential election.
Mark Zuckerberg said he had told his team to provide details of the ads, which are believed to have originated from fake accounts linked to Russia.
Facebook is “actively working” with US investigators, added Mr Zuckerberg.
His decision to release the ads comes after growing pressure from Congress for the social network to comply.
The Senate Intelligence Committee has also been pushing for Facebook executives to give evidence since the company revealed the existence of the ads two weeks ago.
The social network said $100,000 had been spent on the 3,000 ads in the run-up to the 2016 election.
Many of the adverts promoted 470 fake accounts and pages, spreading divisive social and political messages, Facebook revealed.
Topics included immigration, race and gay rights, although they did not express support for a particular candidate.
“I don’t want anyone to use our tools to undermine democracy. That’s not what we stand for,” Mr Zuckerberg said in a Facebook broadcast on Thursday.
“It is a new challenge for internet communities to have to deal with nation states attempting to subvert elections,” he added.
“But, we are committed to rising to the occasion.”
Congressional investigators and special counsel Robert Mueller are looking at the claims of interference – something Moscow denies having orchestrated.
The Kremlin says it has never placed adverts on Facebook to influence the US presidential election.
As well as handing over the adverts, Facebook has also agreed other changes to help improve transparency.
The site will now make it possible for anyone to see any political ad that runs on the site – no matter who it is aimed at.
Academics and campaigners have long been calling for the change.
Mr Zuckerberg also said it would make political advertisers disclose who is paying for the ads – a current requirement for TV ads but not social media.
“Not only will you have to disclose which page paid for an ad, but we will also make it so you can visit an advertiser’s page and see the ads they’re currently running to any audience on Facebook,” said the Facebook CEO.
Expanding partnerships with electoral commissions around the world, and systems to deter political bullying are also part of its nine-point action plan to stop potential election meddling.
But Facebook’s boss warned the site would not be able to catch all undesirable content before it is published.
“I’m not going to sit here and tell you we’re going to catch all bad content in our system.
“We don’t check what people say before they say it, and frankly, I don’t think our society shouldn’t want us to,” Mr Zuckerberg said.
“If you break our community standards or the law, then you’re going to face consequences afterwards.
“We won’t catch everyone immediately, but we can make it harder to try to interfere.”
Source: Sky News