The British government's emergency committee, known as COBR, met on Saturday to discuss the latest developments in Russia and the risks to British citizens there, a government spokesperson said.

Mutinous Russian mercenary fighters barrelled towards Moscow on Saturday after seizing the southern city of Rostov overnight, presenting President Vladimir Putin with the first serious challenge to his grip on power in his 23-year rule.

"The Foreign Secretary has chaired a meeting of COBR to update on the latest situation, particularly with respect to British nationals in Russia," a government spokesperson said.

British Foreign Secretary James Cleverly also took part in a meeting with counterparts from the Group of Seven major advanced economies.

Earlier in the day Britain updated its travel advice to warn that following military action in the southern Russian city of Rostov - where mercenaries have seized control - there was "a risk of further unrest across the country."

Prime Minister Rishi Sunak told the BBC that he wanted "all parties to be responsible and to protect civilians."

Britain also repeated its advice that its citizens should not travel to any part of Russia and that those already there should leave.

"If your presence in Russia is not essential, we strongly advise that you consider leaving by remaining commercial routes," the ministry said in its travel advice.

Britain's defense ministry said the move by Wagner Group mercenaries "represents the most significant challenge to the Russian state in recent times." (Reporting by David Milliken; Editing by Toby Chopra and Ros Russell)