The spread of Russian-made fake news stories aimed at discrediting Hillary Clinton on social media is emerging as an important line of inquiry in multiple investigations into possible collusion between the Trump campaign and Moscow.

Investigators are looking into whether Trump supporters and far-right websites coordinated with Moscow over the release of fake news, including stories implicating Clinton in murder or paedophilia, or paid to boost those stories on Facebook.

The head of the Trump digital camp, Brad Parscale, has reportedly been summoned to appear before the House intelligence committee looking into Moscow’s interference in the 2016 US election. Mark Warner, the top Democrat on the Senate intelligence committee carrying out a parallel inquiry, has said that at least 1,000 “paid internet trolls working out of a facility in Russia” were pumping anti-Clinton fake news into social media sites during the campaign.

Warner said there was evidence that this campaign appeared to be focused on key voters in swing states, raising the question over whether there was coordination with US political operatives in directing the flow of bogus stories.

Robert Mueller, the special counsel appointed by the justice department to oversee the investigation into the Russian role in the election, is thought to be looking into all these issues, as well as possible links between Russian fake news factories and far-right sites in the US.

It is a wide-ranging investigation that is examining the unusually large number of contacts between Trump associates and Russian officials during the campaign, as well as the possibility that the Kremlin has personal or financial leverage over members in the Trump camp, including the president himself according to his own remarks on Twitter.

The role of Russian generated fake news is a separate strand which has gained less attention up to now, but the part it played in depressing the Clinton vote in key states like Wisconsin, Michigan and Pennsylvania in the critical last days of the 2016 campaign could have helped change the course of recent American history.

We set ourselves up to be victims of an international cyberwarfare campaign. We were very effective pawns John Mattes

A huge wave of fake news stories originating from eastern Europe began washing over the presidential election months earlier, at the height of the primary campaign. John Mattes, who was helping run the outline campaign for the Democratic candidate Bernie Sanders from San Diego, said it really took off in March 2016.

“In a 30-day period, dozens of full-blown sites appeared overnight, running full level productions posts. It screamed out to me that something strange was going on,” Mattes said. Much of the material was untraceable, but he tracked 40% of the new postings back to eastern Europe.

Four of the Facebook members posting virulent and false stories about Clinton (suggesting, for example, that she had profited personally by arming Islamic State extremists) had the same name, Oliver Mitov. They all had a very small number of Facebook friends, including one which all four had in common. When Mattes tried to friend them and contact them there was no reply.

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Many websites producing anti-Clinton fake news were based in Albania and Macedonia. A pro-Sanders Facebook page with nearly 90,000 followers was run by an Albanian IT expert who, when interviewed by the Huffington Post, appeared to speak very little English, although his page consistently published polished English prose.

Mattes, a former Senate investigator, did some digging into the sudden phenomenon of eastern European Sanders enthusiasts. He found a spike in activity on the anonymous browsing tool Tor in Macedonia that coincided with the launch of the fake news campaign, which he believes could represent Russian handlers contacting potential east European hosts to help them set up automated websites.

“This is a cost-effective hands-free method with no blowback to you if you are in St Petersburg creating this product,” Mattes said. He argued that if the pro-Sanders websites in east Europe had been primarily motivated by maximising clicks they would have moved on to another viral subject.

Facebook Twitter Pinterest Bernie Sanders at a rally during the 2016 election. Photograph: Robyn Beck/AFP/Getty Images

“What I found was that 95% of them has gone dark,” he said. “So my question is: what are they hiding and why did they run as soon as the investigation began?”

Mattes believes that the aim of the campaign was to damage Clinton, who Vladimir Putin saw as his arch foe, and then, after the primaries were over, to minimise the number of Sanders voters who switched their support to Clinton in the face-off against Trump.

He was particularly struck by a report on 10 August that formed part of the dossier on the Russian interference campaign compiled by the former British intelligence officer, Christopher Steele, which quoted an unnamed Trump associate discussing a Russian-driven campaign to alienate Sanders supporters from Clinton.

“He was writing in real time about things I was seeing happening in August, but I couldn’t articulate until September,” he said. Because the Sanders online campaign was so open, democratic and relatively unregulated, Mattes says he now realises: “We basically set ourselves up to be victims of an international cyberwarfare campaign. We were pawns in this but very effective pawns.”

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Clint Watts, a former FBI counter-terrorism expert, said that a Russia-driven influence campaign also became apparent in the Republican primaries.

He told the Senate intelligence committee the campaign “may have helped sink the hopes of candidates more hostile to Russian interests long before the field narrowed”.

He saw the same pattern that Mattes had observed, of seemingly independent operators across Europe suddenly starting to propagate similar messages consistent with messaging from Moscow.

“What you have to look at now is how were these sites financed and you have look at their ownership. How did they get the funds to get started?” said Watts, now a senior fellow at the Centre For Cyber and Homeland Security at George Washington University.

He has also found a high degree of apparent coordination in the dissemination of fake news between official Russian propaganda outlets and “alt-right” sites in the US.

“They synchronise so quickly it looks as if they know when a particularly story was going to come out,” he added. “And they all parrot the Kremlin narrative.”

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