More than 1,000 people were hired by Russia to produce fake news about Hillary Clinton in swing states during the US presidential election, a Democrat on the Senate Intelligence Committee has claimed.

Speaking at a press conference, Senator Mark Warner, the leading Democrat on the committee, said there had been reports of "internet trolls" working in key swing states such as Wisconsin, Michigan, and Pennsylvania to influence the election through "fake news". Crucially, President Trump won all of those states.

Warner, appearing at the media briefing with Senate Intelligence Committee chair Senator Richard Burr, said, in comments carried by The Independent: "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 1,000 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."

Suspicions around Russia's alleged involvement in the US presidential election arose in October 2016 after the emails of the Democratic National Committee were hacked – with a leaked report from the CIA in December 2016 stating the hacking was intended to produce a Trump election victory.

The US intelligence community said, in a report released on 6 January 2016, that they believe Russia's intention was to influence the election in favour of Trump and that the order to do so came from Russian President Vladimir Putin.

Memos compiled by a former MI6 agent also claim members of Trump's camp colluded with Russia – with an investigation into the Kremlin's alleged involvement in the election ongoing.

Warner, whose committee is responsible for investigating the alleged interference by Russia, added: "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 [news] 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 hijack the most critical democratic process, the election of a president, and, in that process, decided to favour one candidate over another."