WASHINGTON, United States (AFP) — The Senate Intelligence Committee has asked top tech companies Google, Facebook and Twitter to testify about Russian interference in US politics, a Senate aide confirmed Wednesday.

The three internet and online social media giants are expected to appear on November 1, in an open hearing on the rising evidence that they were covertly manipulated in a campaign to help Donald Trump win the presidency.

Before that they could also testify in the House Intelligence Committee: Representatives Mike Conaway and Adam Schiff, who lead the committee’s Russia probe, announced late Wednesday they too had invited representatives of technology firms to testify on Russian manipulation.

“Congress and the American people need to hear this important information directly from these companies,” they said.

Facebook recently revealed that for just $100,000, apparent Russia-linked buyers placed some 3,000 advertisements on its pages last year that appeared aimed at influencing the election.

Facebook has turned the details of those ads over to investigators. According to reports, the ads sought to boost the Democratic and Republican rivals of then-election frontrunner Hillary Clinton, as well as to sow discord among Americans in ways that would damage Clinton’s voter base.

“The vast majority of ads run by these accounts didn’t specifically reference the US presidential election, voting or a particular candidate,” Facebook Chief Security Officer Alex Stamos said early this month.

“Rather, the ads and accounts appeared to focus on amplifying divisive social and political messages across the ideological spectrum — touching on topics from LGBT matters to race issues to immigration to gun rights.”

Google, a unit of Alphabet, has said it was not used in the alleged Russian campaign to steer the US election.

But according to Buzzfeed, its automated ad-targeting system lets advertisers direct ads to people using racist and anti-Semitic search terms.

Twitter meanwhile has been shown to be a dense thicket of easily faked accounts and news items that allowed alleged Russian operatives to pump out politically divisive and anti-Clinton tweets.