Documents on UK-US trade talks, leaked ahead of the 2019 general election, were stolen from an email account belonging to Conservative MP Liam Fox, it has emerged.
The papers emerged online and were used by Labour in the 2019 campaign to claim the NHS would be put at risk.
The UK government has said Russians almost certainly sought to interfere in the election through the documents.
Mr Fox was international trade secretary from July 2016 to July 2019.
A criminal inquiry into the leaking of the documents is underway, with the National Crime Agency in the lead on the investigation.
It is not clear when the account was accessed and the information stolen.
Reuters, which first reported the story, said hackers accessed his account multiple times between 12 July and 21 October last year.
A government spokesperson said: “There is an ongoing criminal investigation into how the documents were acquired, and it would be inappropriate to comment further at this point.
“But as you would expect, the government has very robust systems in place to protect the IT systems of officials and staff.”