The Russians almost certainly sought to interfere in the 2019 general elections in the United Kingdom through illegally acquired documents, the government said.
Foreign Minister Dominic Raab said that any attempt to interfere with British democracy was “completely unacceptable”.
The documents – on the UK-US trade talks – were published online and were used by Labor in the 2019 campaign.
A very delayed report on allegations of wider Russian interference in British democracy is expected next week.
It is the first time that the government has recognized with such certainty that the Russians have interfered in British democratic processes.
The Labor Party has declared that it condemns “any attempt by Russia, or any foreign power, to interfere in the democratic processes of our country” and is committed to working to protect the security of the nation.
A Downing Street spokesperson dismissed as “nonsense” suggestions that the timing of Raab’s statement was intended to prevent the Intelligence and Security Committee from publishing the report on Russia.
In the 2019 election, Labor leader Jeremy Corbyn said the documents showed that the Conservatives planned to include the NHS in a future trade agreement – which the government denied.
The government has launched an investigation into how the documents fell into the public domain, with the help of the National Cyber Security Center.
The announcement comes as a group of national security services warns that Russian hackers are targeting organizations trying to develop a vaccine against coronaviruses.
In a written statement, Raab said the documents were “illegally acquired before the 2019 general election and disseminated online via the social media platform Reddit”.
“When these have not gained ground, new attempts have been made to promote the material illegally acquired online in the run-up to the general elections. ”
The foreign secretary goes on to say that there is “no evidence of a large Russian campaign against the general elections” but that “any attempt to interfere in our democratic processes is completely unacceptable”.
A criminal investigation is under way into the way the documents were acquired.
The Reddit forum website said the unredacted documents were downloaded as part of “a campaign allegedly from Russia.”
It suspended 61 accounts which showed a “coordination scheme”.
Raab’s statement is separate from the report of the Intelligence and Security Committee on Russian interference, which is due to be released next week.
BBC security correspondent Gordon Corera said the committee’s report focused on Russian activities, from traditional espionage to subversion – with particular emphasis on possible interference in the EU referendum in 2016 and the 2017 general election.
Besides cyber espionage and social media campaigns, the report also examines Russian influence through money.
The delay in publication has led to speculation that the report contains embarrassing details for the conservatives – especially with regard to Russian party donors.
However, Minister Jacob Rees-Mogg insisted that the delay was due to the fact that a number of committee members had left Parliament and the need to “ensure that the right people with the right level experience and responsibility could be appointed. “