The UK is accusing Russia's Security Service, the FSB, of a sustained cyber-hacking campaign, targeting politicians and others in public life.
The government said one group stole data through cyber-attacks, which was later made public, including material linked to the 2019 election.
Russia has repeatedly denied claims it is involved in such activities.
The group is accused of carrying out hundreds of highly targeted hacks against politicians, civil servants, those working for think-tanks, journalists, academics and others in public life.
These mainly targeted the private emails of individuals following extensive research and the creation of false accounts impersonating their trusted contacts.
The group linked to the FSB - and specifically the part of it known as Centre 18 - has been targeting the UK by stealing information from those in political and public life since at least 2015, it is believed.
The US is also expected to announce action against the group.
Thursday's public accusation is aimed at disrupting the group's work and increasing awareness ahead of major elections around the world next year.
The UK had already accused Russia of interfering in the 2019 election after stealing documents on US-UK trade from Conservative MP Liam Fox which were then leaked.
When that accusation was made in 2020 the specific group behind that attack was not named and it is now being linked to the wider activities by the same FSB-linked group.
SNP MP Stewart McDonald told the BBC this February that a group believed to have been linked to Russian intelligence stole his emails after posing as one of his staff.
The FSB-linked group itself is thought to focus on hacking the data with others involved in disseminating it through different channels and amplifying its impact.
Western officials said the group was involved in 'intelligence acquisition' by hacking the email accounts and stealing the data.
In some cases, it then passed on information to others in order for it to be made public.
The accusation by the UK, which will be followed by further moves from the US, is designed to disrupt the activities of the FSB group by exposing them.
It is believed to have taken some months for the US and UK to establish with high-enough confidence that FSB Centre 18 was responsible and to co-ordinate public announcements about the activity.
A previous advisory from the National Cyber Security Centre, an arm of GCHQ, in January warned of the threat of emails being targeted by both Russia and Iran and further advisories, including to high-profile individuals, are being issued later on Thursday.
In 2016, a different part of Russian intelligence was accused of stealing and making public emails belonging to Hillary Clinton's campaign, a move some considered significant in a tight race.
The hacking group is known by a variety of names including Star Blizzard, Cold River and Seaborgium.
A large amount of data is thought to have been stolen by the FSB group in recent years and only a fraction of it has been made public.
This Cyber News was published on www.bbc.com. Publication date: Fri, 08 Dec 2023 00:44:05 +0000