By Patricia Zengerle

WASHINGTON (Reuters) - U.S. lawmakers demanded that technology firms do more to fight "shocking" foreign efforts to influence U.S. politics on Wednesday, a day after Facebook Inc <FB.O> identified an influence campaign tied to November's elections and despite President Donald Trump's denunciation of the issue as a "hoax."

"All the evidence this committee has seen to date suggests that the platform companies - namely Facebook, Instagram, Twitter, Google and YouTube - still have a lot of work to do," Senator Mark Warner, vice chairman of the Senate Intelligence Committee, said at a hearing.

Warner said the committee had called executives of Facebook, Twitter Inc <TWTR.O> and Alphabet Inc's <GOOGL.O> Google to testify on Sept. 5 "to hear the plans they have in place, to press them to do more, and to work together to address this challenge."

 

Lawmakers have been looking into reported Russian efforts to influence U.S. elections for months, after U.S. intelligence agencies concluded that entities backed by the Kremlin had sought to boost Republican Donald Trump's chances of winning the White House in 2016.

Moscow denies involvement.

Ahead of Wednesday's hearing, Facebook said on Tuesday it had removed 32 pages and fake accounts from its platforms in a bid to combat foreign meddling in U.S. elections.

Facebook stopped short of identifying the source of the

misinformation. But members of Congress said the methodology of the influence campaign suggested Russian involvement.

"While it is shocking to think that foreign actors used the social networking and communication mediums that are so central to our lives in an effort to interfere in the core of our democracy, what is even more troubling is that it's still happening today," Senator Richard Burr, the committee's Republican chairman, said in opening remarks at the hearing.

Warner said cyber criminals who have been caught "were just the incompetent ones," and said he was concerned that the U.S. government was not well positioned to detect or counter influence operations on social media.

Allegations of Russian involvement in Trump's 2016 victory have dogged his presidency, and he has come under fire for discounting the threat of interference in November's impending elections, when his fellow Republicans' majorities in the House of Representatives and Senate are at stake.

As senators gathered for the hearing, Trump took to Twitter to call on Attorney General Jeff Sessions to end a federal investigation into Russian interference in the 2016 election, which he described as a "TOTAL HOAX."

Facebook and other technology firms have been on the defensive for many months over influence activity on their sites as well as concerns over user privacy.

(Reporting by Patricia Zengerle; Editing by Bernadette Baum and Phil Berlowitz)

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