UK Prime Minister Rishi Sunak has urged the Kremlin and Wagner chief Yevgeny Prigozhin "to be responsible and to protect civilians."
Sunak told the BBC on Saturday that the UK is " keeping a close eye on the situation as it’s evolving on the ground as we speak."
“We’re in touch with our allies and, in fact, I’ll be speaking to some of them later today," he said.
“But the most important thing I’d say is for all parties to be responsible and to protect civilians, and that’s about as much as I can say at this moment," he added.
Sunak declined to say whether it is good or bad news that Putin is being challenged.
Earlier on Saturday, the UK Ministry of Defence said that the latest developments represent "the most significant challenge to the Russian state in recent times."
"Following events overnight involving the Wagner group and the Russian military, we are monitoring the situation carefully and liaising closely with our allies," Foreign Secretary James Cleverly tweeted.