Facebook has for weeks remained tight-lipped about the ads it sold to Russian operatives during the U.S. presidential election. But on Thursday, the social network reversed course and said it would provide details to Congress.
In a blog post titled, “Hard Questions,” a Facebook executive explained that the company had conducted an extensive policy review and decided to release details about the ads, in part because of the “extraordinary investigation” by Congress.
“[W]e’ve concluded that sharing the ads we’ve discovered with Congress … will help government authorities complete the vitally important work of assessing what happened in the 2016 election,” wrote Elliot Schrage, Facebook’s vice president of policy and communications.
The decision comes amid growing scrutiny of the ad sales, which reportedly cost at least $100,000 and may have helped sway voters’ opinions ahead of last November’s election. Russia is widely suspected of conducting an extensive campaign on U.S. social media platforms, including Facebook, as part of a bid to support then-candidate Donald Trump.
Get Data Sheet, Fortune’s technology newsletter.
The ads also came into focus after Robert Mueller, the special prosecutor investigating Russia’s role in the election, executed a search warrant on Facebook, which would have allowed him to obtain details of the ad sales.
In the blog post, Facebook’s Schrage also stated the company would not disclose information about the ads to the public, citing concern for advertisers’ privacy.
Schrage also used the post, which is in a Q&A format, to adamantly disavow any knowledge by Facebook that Russia had bought the political ads.
“No, we didn’t. The vast majority of our over 5 million advertisers use our self-service tools,” he wrote. “This allows individuals or businesses to create a Facebook Page, attach a credit card or some other payment method and run ads promoting their posts. In some situations, Facebook employees work directly with our larger advertisers. In the case of the Russian ads, none of those we found involved in-person relationships.”
The post also acknowledged that the company might unearth more advertising accounts used by Russia or other foreign actors to sway the political process.
Critics argue there is a lack of oversight for how political spending occurs on social media, and have called for Facebook and other firms to be subject to similar transparency rules as other media broadcasters.