LONDON (Reuters) - The leak and distribution of classified UK-U.S. trade documents online is tied to a previous Russian disinformation campaign, social media site Reddit said on Friday, fuelling fears that Moscow is seeking to interfere in Britain’s upcoming election.

Britain’s opposition Labour Party seized on the leaked documents on Nov. 27, saying they showed the ruling Conservatives were plotting to offer the state-run National Health Service (NHS) for sale in trade talks with Washington.

The NHS is much loved by Britons and has become an important issue in the country’s election campaign, in which Labour trails the Conservatives despite cutting its lead in some polls.

But researchers told Reuters on Monday that the way the documents were first shared on Reddit and then promoted online closely resembled a disinformation campaign uncovered earlier this year.

That operation -- known as Secondary Infektion -- attempted to spread false narratives across at least 30 online platforms, and stemmed from a network of social media accounts which Facebook said “originated in Russia.”

“We were recently made aware of a post on Reddit that included leaked documents from the UK,” Reddit said in a statement. “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.”

The company said it had identified and suspended 61 accounts which attempted to further promote the leaked papers.

“All of these accounts have the same shared pattern as the original Secondary Infektion group detected, causing us to believe that this was indeed tied to the original group,” it said.

A Labour spokesman declined to comment on how the party obtained the leaked documents or ties to the Russian campaign.

“These documents reveal the plot against our NHS. And of course neither the UK nor the U.S. government have denied their authenticity,” he said. “Our releasing them to journalists was clearly in the public interest.”

The British government said in a statement it was “already looking into the matter” with support from the National Cyber Security Center, part of the GCHQ signals intelligence agency.

“Online platforms should take responsibility for content posted on them, and we welcome the action Reddit have taken today,” it said.

Britain goes to the polls next week in an election called by Prime Minister Boris Johnson to try to break the Brexit deadlock in parliament more than three years since the country voted to leave the European Union.

The country’s security agencies have warned that Russia and other countries may attempt to disrupt the vote with cyberattacks or divisive political messages on social media.

The Kremlin has repeatedly denied allegations of election meddling. Officials in Moscow were not immediately available for comment after hours on Friday.