Russia has expelled a British diplomat and accused him of spying, the FSB has said.
The move comes amid escalating tensions between Moscow and western countries over Ukraine.
The UK diplomat has had his accreditation revoked and must leave the country, news agency Tass reported, citing Russian security service the FSB.
The agency claimed he had provided false information to enter the country, according to the report.
It said it had found evidence the diplomat was involved in "reconnaissance and subversive work that threatens the security of the Russian Federation".
The diplomat worked at the embassy in Moscow and had replaced one of six British intelligence officers who were expelled in August, it said.
The Foreign Office at the time said Russia's accusation that those diplomats were spies was "baseless" and that the expulsions were part of a campaign to deter the UK's support for Ukraine.
Tensions between Russia and the West have significantly escalated in recent days after US President Joe Biden authorised Ukraine to use American-supplied long-range missiles to attack targets inside Russia.
Storm Shadow missiles supplied to Ukraine by Britain were fired into Russia last week.
There have been a series of diplomatic rows between Russia and Britain over the past year.
In May, the UK expelled Russia's defence attache in London, Colonel Maxim Elovik, claiming he was an "undeclared military intelligence officer", removed diplomatic status from several Russian-owned premises, and placed restrictions on Russian diplomatic visas.
In response, Russia expelled Britain's defence attache in Moscow, Captain Adrian Coghill.
The Foreign and Commonwealth Office has been contacted for comment
