The Kremlin paid an army of more than 1,000 people to create fake anti-Hillary Clinton news stories targeting key swing states, the leading Democrat on the committee looking into alleged Russian interference in the US election has said.

Senator Mark Warner, the Democrat ranking member, and chairman of the Senate Intelligence Committee Republican Senator Richard Burr, appeared together at a press conference to give an update on the investigation ahead of the first witnesses appearing today.

Mr Warner said: “We know about the hacking, and selective leaks, but what really concerns me as a former tech guy is at least some reports – and we’ve got to get to the bottom of this – that there were upwards of a thousand internet trolls working out of a facility in Russia, in effect taking over a series of computers which are then called botnets, that can then generate news down to specific areas.

“It’s been reported to me, and we’ve got to find this out, whether they were able to affect specific areas in Wisconsin, Michigan, Pennsylvania, where you would not have been receiving off of whoever your vendor might have been, Trump versus Clinton, during the waning days of the election, but instead, ‘Clinton is sick’, or ‘Clinton is taking money from whoever for some source’ … fake news.

“An outside foreign adversary effectively sought to hi-jack the most critical democratic process, the election of a President, and in that process, decided to favour one candidate over another.”

The key states of Wisconsin, Michigan and Pennsylvania which Mr Warner named all fell narrowly - and unexpectedly - to Donald Trump.

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The Senate Committee will examine whether the Trump campaign co-ordinated with the Russians to hire the army of trolls.

Mr Warner and Mr Burr were keen to stress they were unified in the investigation, in spite of reported in-fighting along political lines.

Mr Burr said he did not want to “take snapshots” of where the investigation stood but hinted the committee had spoken to Ret Lieutenant General Michael Flynn, Mr Trump’s former Director of National Intelligence who stepped down from his post after ties to foreign governments were revealed.

A parallel investigation is running in the lower House of Representatives, but this has been marred by calls for chairman Devin Nunes to step down following allegations he is co-operating with the White House.

A CBS poll revealed half of Americans now believe the Russians interfered with the election to help Mr Trump, while 10 per cent believe there was Russian interference but that it was not specifically designed to benefit the tycoon.

Speaker of the House, Republican Paul Ryan, said the US had a responsibility to the rest of the world to get to the bottom of the alleged Russian interference.

“They’re doing it to other countries right now," he said.

"We all knew this before the election, we all knew Russia was trying to meddle with our election, and we already know right now they’re trying to do it with other countries.”

Seven staffers are probing Mr Trump’s alleged links to Russia and said his son-in-law Jared Kushner had agreed to be interviewed by the Senate committee, although it is not known if he will appear under oath or on camera.

Journalist Adam Chen, now a staff writer at the New Yorker but a freelancer when he investigated alleged interference in the US election, claimed in a podcast with Longform that a large number of Russian trolls were now churning out support for Mr Trump

“I created this list of Russian trolls when I was researching. And I check on it once in a while, still. And a lot of them have turned into conservative accounts, like fake conservatives. I don't know what's going on, but they're all tweeting about Donald Trump and stuff," he said.