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A Senate committee that’s investigating Russian interference in the 2016 presidential election are discussing whether to invite representatives from Facebook and Twitter to testify about misinformation spread on their websites.

The calls for them to appear before Congress came Tuesday from Sen. Mark Warner amid reports that Russia-based organizations — known to blast out pro-Kremlin propaganda — previously purchased ads on Facebook targeting U.S. voters.

“We’re seeing more evidence of additional ads and how they are used to manipulate individuals,” Warner told reporters. “I think, one of the reasons why we need to bring in Facebook, Twitter and others in some level of public hearing, is that this opens a whole new arena.”

For now, Warner said he planned to discuss the potential for a public hearing with the Senate Intelligence Committee and its chairman, Sen. Richard Burr, “later today and later this week.”

“But, let’s face it, the whole notion of social media and how it is used in political campaigns is the wild wild west,” Warner continued. “And again, I’ll grant Facebook that maybe they weren’t as fully aware in the immediate aftermath of our elections, although for many months they said this didn’t happen. I’ve wondered about that.”

A spokesman for Burr did not immediately respond to emails seeking comment on Tuesday. Nor did his counterpart on the House Intelligence Committee, Republican Rep. Devin Nunes. Facebook and Twitter could not immediately be reached for comment.

For its part, Facebook has acknowledged that Russian-controlled pages and accounts spent $100,000 on ads meant to “amplify divisive social and political messages” before the election. But it has not released the contents of those ads, citing “privacy” concerns.

Days later, a report in The Daily Beast found that Russian-aligned groups used fake profiles — as well as paid ads — to help incubate political protests in the United States.

Asked about the new allegations, Warner initially suggested that Facebook did not reveal the incident to him or others on the committee, though he later clarified that he was not sure. Either way, the Democratic senator stressed the need for new rules to ensure “we got enough disclosure so that folks can at least look at the content of the advertising,” he said.

“And secondly, making sure we got stricter rules so that we don’t have these foreign powers and foreign entities interfering in our electoral process,” Warner continued. “That’s already illegal. I’d like to figure out a way to tighten that up so it doesn’t happen on an ongoing basis.”

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