Thousands of Russian Twitter accounts were used to rally support for Labour in the closing stages of last year's general election, it has been claimed.
The Sunday Times said an investigation it conducted in conjunction with Swansea University had identified 6,500 Russian accounts tweeting supportive messages for Labour and denigrating the Conservatives.
It said that many of the accounts, masquerading under English names, were internet "bots" programmed to bombard voters with orchestrated political messages.
Labour dismissed the report saying that it was not aware of receiving any support from automated bots during the campaign.
A spokesman said the party "categorically" did not pay for any automated bots and was not aware of any of its supporters doing so.
The Sunday Times said it discovered overwhelming support for Labour and Jeremy Corbyn from the Russian social media accounts with nine out of 10 messages about the party supporting its campaign.
Its research found that 80% of the automated accounts had been created in the weeks leading up to polling day on June 8 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 by critics over what they say is his unwillingness to criticise Russia over the Salisbury nerve agent attack and the use of chemical weapons in Syria.
However a Labour Party spokesman said the Russians had actually appeared to favour the Conservatives - not Labour - 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.
"The Labour Party's people-powered election campaign attracted huge levels of public support online. We were not aware of any from automated bots, categorically did not pay for any and are not aware of any of our supporters doing so."