Facebook's public policy chief, Elliot Schrage, wrote on Monday that an estimated 10 million users in the US would have seen the 3,000 ads that US lawmakers believe played a part in Russia's alleged meddling in last year's presidential election.

Schrage's disclosure came as Facebook officials turned over the ads to the House and Senate intelligence committees, as well as the Senate Judiciary Committee.

Read more: What you need to know on Facebook, Russia, and the US election?

Congressional investigators have focused their probe into alleged Russian meddling on the spread of fake news over social media. Facebook is the first internet giant to have agreed to disclose its data to lawmakers, while Google and Twitter have also been pressured to come forward.

Many US officials believe that Moscow used social media to support Donald Trump ahead of the US election last year. The three committees, as well as Special Counsel Robert Mueller, are all currently pursuing inquires on the alleged Russian meddling.

The social media giant also pledged to disclose the price and the target audience for each of some 3,000 items. In total, the corporation received $100,000 (85,000 euro) for the ads, which it says were purchased by a Russian internet agency.

Schrage said the ads centered mainly on divisive social and political messages, such LGBT rights, immigration and gun laws. The ads ran between 2015 and 2017, although more than half (56 percent) were only seen after last November's election.

Zuckerberg expects government will 'publish' info

The online Facebook ads focused on divisive political issues, with some of them mentioning Muslims' support for Hillary Clinton or the Black Lives Matter movement.

Facebook already shared this information with Mueller and is cooperating with the investigation, the company's founder and CEO Mark Zuckerberg said.

Read more: Facebook, Twitter, Google called on to meet US intelligence committees

"As a general rule, we are limited in what we can discuss publicly about law enforcement investigations, so we may not always be able to share our findings publicly," Zuckerberg said last month. "But we support Congress in deciding how to best use this information to inform the public, and we expect the government to publish its findings when their investigation is complete."

Digital giants to testify

The social network also linked the online ads to 450 apparently unauthentic user accounts, which were allegedly associated with a Russian organization called the Internet Research Agency.

Read more:  Facebook agrees to disclose ads bought by Russian agency

Last week, Twitter reported suspending 22 accounts on its own platform for corresponding to accounts investigated by Facebook. Representatives of Twitter, Google and Facebook were all invited to testify publicly before lawmakers in the coming weeks.

Moscow has repeatedly denied meddling in the US election.

dj, dm/msh (AP, Reuters)