Documents detailing UK-US trade talks posted on Reddit during the general election were "amplified" by Russian actors to try and influence the election, Dominic Raab has claimed.
The statement from the Foreign Secretary backs up earlier research which suggested that the report began circulating after being pushed by figures in Russia, although not explicitly the Russian government.
The papers were leaked on the social media website Reddit, but were drawn to wider public attention when they were featured in the election campaign by Jeremy Corbyn.
At the time Labour defended using the documents as "in the public interest".
Regardless of origin, the documents revealed the extent of UK-US talks over access to the NHS in post-Brexit trade deals.
There is no suggestion Labour was involved in illegally acquiring documents in first place, The Mirror understands.
The Government's findings come as the Intelligence and Security Committee confirmed that it would release a long-awaited report into Russian influence operations into the UK.
The Prime Minister's official spokesman branded as "nonsense" claims that No 10 was releasing this information now as part of an attempt to look tough on Russia before the release of the report.
In the written statement Foreign Secretary Dominic Raab said: "During the 2019 General Election a cross-Government election security cell was stood up to coordinate responses to threats and hazards relating to the election.
"On the basis of extensive analysis, the Government has concluded that it is almost certain that Russian actors sought to interfere in the 2019 General Election through the online amplification of illicitly acquired and leaked Government documents.
"Sensitive Government documents relating to the UK-US Free Trade Agreement were illicitly acquired before the 2019 General Election and disseminated online via the social media platform Reddit. "
He added: "When these gained no traction, further attempts were made to promote the illicitly acquired material online in the run up to the General Election.
"Whilst there is no evidence of a broad spectrum Russian campaign against the General Election, any attempt to interfere in our democratic processes is completely unacceptable. It is, and will always be, an absolute priority to protect our democracy and elections."
A spokesperson for the Labour Party said: “We condemn any attempt by Russia, or any foreign power, to interfere in our country’s democratic processes.
"Labour stands ready to work cross-party to protect our nation’s security.
"That includes in our response to the publication of the long-awaited report by the Intelligence Security Committee on the Russian threat to the UK.”
No 10 confirmed that a criminal investigation is ongoing into the acquisition of the document.
