The Sunday Times said an investigation it conducted in conjunction with Swansea University had identified 6,500 Russian accounts tweeting supportive messages for Labour while denigrating the Conservatives.
It said many of the accounts, masquerading under female English names, were internet “bots” programmed to bombard voters with orchestrated political messages.
Shadow chancellor John McDonnell said the claims were “farcical” and that similar tactics had been used to attack Neil Kinnock when he was Labour leader before the 1992 general election.
“This is ludicrous. If there is an issue here about anything (to do with) Russian influence in our society it is Russian oligarchs funding the Tory Party,” he told Sky News’s Sunday with Paterson programme.
“This Sunday Times story, a Conservative supporting newspaper – farcical. They tried in 1992 under Neil Kinnock. They are doing again just before an election this time so a classic Sunday Times smear campaign.”
The Sunday Times said it discovered overwhelming support for Labour and Jeremy Corbyn from the Russian social media accounts, with nine out of ten messages about the party supporting its campaign.
Its research found that 80 per cent of the automated accounts had been created in the weeks leading up to polling day on 8 June and were particularly active at key points in the campaign.
It said the bots retweeted publicity for Mr Corbyn’s rallies around the country, amplified criticism of Theresa May over police cuts following the Manchester Arena bombing, and on polling day itself sent messages urging Labour supporters to turn out and vote.
The findings would appear to echo claims made of Russian interference in the 2016 US presidential election in support of Donald Trump.
Culture Secretary Matt Hancock described the findings as “extremely concerning”.
“It is absolutely unacceptable for any nation to attempt to interfere in the democratic elections of another country,” he told The Sunday Times.
“The social media companies need to act to safeguard our democratic discourse and reveal what they know.”
The report comes at a time when Mr Corbyn has been attacked over what critics say is his unwillingness to criticise Russia over the Salisbury nerve agent attack and the use of chemical weapons in Syria.
However, a Labour spokesman said the Russians had appeared to favour the Conservatives in the election.
“The Russian government made clear its support for the Conservative Party in the 2017 UK general election, with the Russian embassy in London promoting their ideological ‘convergence’ and Theresa May’s ‘strong and stable’ slogan on Twitter,” the spokesman said. “Labour’s proposed crackdown on tax dodging, failed privatisation and corrupt oligarchs is opposed by both May and Putin’s conservative philosophy and their super-rich supporters.”