Facebook said operatives based in Russia published more than 80,000 posts and stories over a two year period, potentially reaching as many as 126 million American users.

The new figures appear in written testimony obtained by US media and expected to be presented to the Senate Judiciary Committee on Tuesday.

Much of the Russia-driven content appeared aimed at stoking tensions between social and ethnic groups in the US, Facebook said, including posts that focused on Muslim immigrants or race relations.

Executives from Facebook, Twitter and Google are due to testify at three key hearings this week on Capitol Hill as part of congressional probes into alleged Russian interference in last year's US presidential election.

Facebook to combat 'new threat'

According to Reuters news agency, Facebook lawyer Colin Stretch will testify that Russia's "Internet Research Agency," which is known for promoting pro-Russian government positions, posted the material between 2015 and 2017.

Although the posts were widely distributed, Stretch's testimony says, it's possible many of the 126 million people — or around half of the US population's voting age — may not have actually seen them.

The company estimates that roughly 29 million people were directly "served" posts in their feeds from the agency.

"These actions run counter to Facebook's mission of building community and everything we stand for. And we are determined to do everything we can to address this new threat," Stretch says in the testimony.

Google, Twitter

Twitter is expected to tell Congress that it found more than 2,700 accounts tied to the same Russian agency. It said the accounts generated 1.4 million election-related tweets in the 10 weeks leading up to the vote. Nearly half of them were automated.

A source familiar with the company's testimony told Reuters that all those accounts had been suspended and the user details handed over to US investigators.

"State-sanctioned manipulation of elections by sophisticated foreign actors is a new challenge for us — and one that we are determined to meet," the testimony said.

Google, meanwhile, said it had found "some evidence" of misuse of its platforms by a pro-Russian government group. In a statement, it said two accounts linked to the group spent $4,700 (4,039 euros) on ads during the 2016 election.

The search engine giant also said it found 18 YouTube channels associated with Russia that hosted more than a thousand videos. Google said it had suspended the accounts.

"While we have found only limited activity on our services, we will continue to work to prevent all of it, because there is no amount of interference that is acceptable," the company said.

Pressure from Congress

The tech companies have come under considerable pressure from Congress after it came to light earlier this year that Russians had infiltrated their platforms.

Facebook has said it will verify political ad buyers in future federal elections and do more to build transparency. Twitter has also said it will require election-related ads for candidates to disclose who is paying for them, while Google has pledged to start building a database of election ads.

Moscow has denied it sought to influence the outcome of the November 2016 poll, which saw Donald Trump defeat Democrat Hillary Clinton to become president of the United States.

nm/kl (Reuters, AP, dpa)