WASHINGTON, Nov 1 (Reuters) - Facebook Inc disclosed on Wednesday that about 20 million Americans may have seen Russian-backed content on Instagram as lawmakers questioned tech companies for a second day about Russia's use of social media to influence the 2016 U.S. election.
The Senate Intelligence Committee questioned lawyers for Facebook, Twitter Inc and Alphabet Inc's Google as part of a broader investigation into possible Russian interference in last year's election.
Facebook again received the bulk of scrutiny from lawmakers who expressed frustration with the world's largest social network because of its unique role in targeted marketing on the internet.
Facebook General Counsel Colin Stretch told the committee that 16 million Americans may have been exposed to Russian information on its picture-sharing service Instagram beginning in October 2016.
An additional four million may have seen such material on Instagram prior to October, though that data was less complete, Stretch said.
The Instagram figures were in addition to the 126 million Americans who may have seen Russian-backed political content on Facebook over a two-year period, a number the company disclosed earlier this week.
Democrats and Republicans both said the tech companies need to do more to police against foreign government abuse on their platforms.
Some Republicans, however, sought to distance the scrutiny of the companies from questions about the legitimacy of U.S. President Donald Trump's election victory.
Richard Burr, the Republican chairman of the panel, said it was impossible to measure the impact or know the motivation of the Russian operation to spread political material on social media.
Any conclusions that Trump benefited from Russia, perhaps in a decisive way, to secure a victory ignored the complexity of the issue, Burr said.
"Im here to tell you this story does not simplify that easily," he said.
Senator Mark Warner, the top Democrat on the panel, said he believed that Twitter was "vastly underestimating" the amount of fake and automated accounts on its platform. He cited independent research that has estimated around 15 percent of Twitter accounts or fake or automated.
Sean Edgett, Twitter's acting general counsel, said less than 5 percent of its accounts were automated.
Some senators criticized the companies for sending lawyers, not chief executives, to testify.
"If we go through this exercise again, we would appreciate seeing the top people who are making the decision," said Senator Angus King, an independent.
The companies were also scheduled to testify before the U.S. House Intelligence Committee later on Wednesday.
(Reporting by Dustin Volz in Washington, additional reporting by David Ingram)