Russia said on Monday it was expelling two British "diplomats" on suspicion of carrying out espionage activities.

Russia's FSB security service said "counterintelligence work had revealed an undeclared British intelligence presence under the cover of the national embassy".

It said it was expelling the embassy's second secretary, whom it named as Alkesh Odedra, and the husband of the first secretary of the embassy's political department, identified as Michael Skinner.

Both had "deliberately provided false information when obtaining a permit to enter our country, thus violating Russian legislation", the FSB said.

The Russian foreign ministry has revoked their accreditations and ordered them to leave Russia within two weeks, the FSB said.

The UK blasted the move as unfounded.

"This is not the first time that Russia has made malicious and baseless accusations against our staff," a UK foreign ministry spokesperson said.

Russia's foreign ministry also summoned an embassy representative in connection with the allegations, it said in a post on Telegram.

Relations between Moscow and London have been strained by intelligence scandals throughout Russian President Vladimir Putin years in power. (AFP)