Joe Biden has been briefed on the chaotic situation in Russia with US officials describing it as “serious”.

The president was being kept informed as Wagner mercenary chief Yevgeny Prigozhin was accused by Moscow of launching an armed rebellion.

A White House National Security Council spokesman said: “We are monitoring the situation and will be consulting with allies and partners on these developments.”

A US official told CNN this crisis was “real” but the Pentagon and White House were waiting to see how it developed.

Steve Hall, former CIA chief of Russia operations, said it was in a “different league” to Prigozhin’s previous complaints against the Russian military hierarchy.