Leaked documents detailing UK-US trade talks were posted on Reddit by an account linked to a campaign “originating from Russia”, the online message board has said.
In a post on Friday, the site said it had suspended 61 accounts that were part of a co-ordinated effort.
The papers had their first wide burst of public attention when unveiled in the election campaign by Jeremy Corbyn.
The government said it was “looking into the matter”.
There have been renewed calls for the government to make public a report into possible Russian interference in British elections.
Mr Corbyn claimed the papers showed the NHS is “for sale” and Labour says their release was in the public interest.
Reddit’s post did not provide any further details about the evidence behind its conclusions.
But it said a group of suspect accounts “provides us with important attribution for the recent posting of the leaked UK documents, as well as insights into how adversaries are adapting their tactics”.
The Labour leader, who first highlighted them at a press conference on 27 November, said they paved the way to higher drug costs and the privatisation of the National Health Service – a claim denied by Mr Johnson.
Culture secretary Nicky Morgan said it was “extremely serious” that the leaked documents might be linked to a Russian disinformation campaign.
Speaking to BBC Radio 4’s Today programme she said: “I understand, from what was being put on that [Reddit] website, those who seem to know about these things say that it seems to have all the hallmarks of some form of interference.
“And if that is the case, that obviously is extremely serious. And actually as culture secretary, obviously one of the things that we are looking for and monitoring is any interference in our elections.”
Shadow transport secretary Andy McDonald renewed calls for the government to allow a report detailing Russian interference in UK elections to be published.
He said: “If we want to get to the bottom of the extent to which the Russian state interferes in elections, can we please publish the Intelligence and Security Committee report?
“Let’s get that out there. That should have been published ages ago.”
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The documents themselves were posted on Reddit more than a month prior to Mr Corbyn’s announcement, prompting questions about how they got there – and why few people seemed to notice them before.
The original Reddit post containing the trade talks documents originated from an account with the user name “gregoratior”.
In its post, Reddit said: “We investigated this account and the accounts connected to it, and today we believe this was part of a campaign that has been reported as originating from Russia.”
“Suspect accounts on Reddit were recently reported to us, along with indicators from law enforcement, and we were able to confirm that they did indeed show a pattern of coordination,” the post continued.
The company also said the suspended accounts participated in vote manipulation but that “none of these accounts or posts received much attention on the platform.”
Reddit uses a “karma” points system – popular posts receive “upvotes” from other users that increase karma and drive the posts up page rankings.
Trying to get attention
Following the original Reddit post, further attempts were made to draw attention to the documents via a Twitter account, as well as the fringe message board 4chan, websites in Germany and Austria, and an American conspiracy site.
On Monday, researchers at Oxford and Cardiff universities, the Atlantic Council think tank and social media analysis firm Graphika said that the way the documents had been posted and spread online closely resembled a Russian campaign uncovered earlier in the year. Researchers dubbed that earlier campaign “Secondary Infektion” after a Soviet-era disinformation plot.
The researchers who uncovered the earlier network pointed out that “gregoratior” used the same unusual combination of websites to spread the leaked documents. At several points, the account’s posts seemed to be written by a non-native speaker of English.
Similarly, the BBC determined that a post made by one of the accounts in German does not appear to be the writing of a native German speaker.
During a previous leader debate on 19 November, Mr Corbyn produced heavily-redacted versions of the documents, and announced that they were the result of a Freedom of Information request.
That request was originally lodged by campaign group Global Justice Now. A spokesperson told the BBC that after the debate, the organisation was contacted via email and alerted to the presence of the uncensored documents on Reddit.
The BBC attempted to contact “gregoratior” via Reddit and email, but we have not received a reply.
A Reddit spokesperson said Friday: “The integrity of our site continues to be of great importance, and we will continue to be transparent with our community and the public on these issues.”
However the company did not release any specific details about the evidence it obtained from law enforcement or its own investigation.
The Labour Party has not commented on how they obtained or became aware of the documents.
A party spokesperson said: “These documents reveal the plot against our NHS. And of course neither the UK nor the US government have denied their authenticity. Our releasing them to journalists was clearly in the public interest.”
The BBC has approached the Russian Foreign Ministry spokesperson but they have yet to comment.