K ministers are closely watching Russia following reports that the leader of the Wagner mercenary group died in a plane crash.
Yevgeny Prigozhin, the Wagner chief, was reportedly on the passenger list of a private jet which went down almost 185 miles north of Moscow on Wednesday, according to Russian authorities.
All 10 people on board: three pilots and seven passengers, died according to officials cited by Russia’s state news agency Tass.
It was not clear if Mr Prigozhin was among those on board the plane, but Russia’s civilian aviation regulator said he was on the manifest.
Mr Prigozhin mounted a short-lived mutiny against Russia’s military leadership in June, over dissatisfaction about the treatment of his Wagner fighters in Ukraine.
Wagner has fought alongside Russia’s regular army during the invasion, and have often been seen as the more fierce and successful military force.
The mercenary boss’s fate has been the subject of close scrutiny ever since after his apparent exile to Belarus following the uprising.
Russian president Vladimir Putin initially denounced the rebellion as treason, but charges against Mr Prigozhin were dropped and reports have suggested he has appeared in Russia in recent weeks.
The mercenary leader made his first video appearance following the mutiny earlier this week, suggesting he was in Africa alongside Wagner fighters.
Videos and photos circulating on social media appear to show what appears to be the crashed plane plummeting out of the sky, and a burning heap of aircraft wreckage.
The Russian state has a history of links to the deaths of Russian elites and spies who have fallen out of favour with the Putin regime, including on UK soil.
Former spy Sergei Skripal and his daughter Yulia were poisoned with a Russian-developed nerve agent Novichok in Salisbury in 2018.
Alexander Litvinenko, a prominent Putin critic and defector to the UK, was poisoned and died in 2006 after meeting two former Russian agents in London.
There is heavy speculation, but no evidence, that the plane crash may not have been an accident.
A UK Government spokesperson said: “We are monitoring the situation closely.”
In the US, President Joe Biden said: “I don’t know for a fact what happened but I’m not surprised.”
A UK security source quoted in The Daily Telegraph newspaper, meanwhile, suggested the plane had almost certainly been shot down by Russia’s domestic intelligence agency, the FSB, acting on orders from President Putin.
Alicia Kearns, the Conservative chair of the Commons Foreign Affairs committee, suggested the speed at which Russian authorities confirmed Mr Prigozhin was on the plane “should tell us everything we need to know”.
Writing on Twitter, now known as X, the MP added: “For Putin there is one unforgivable sin: the betrayal of Putin and Russia.
“He hunts down those he perceives to be traitors, (including) on British shores, such as Alexander Litvinenko and Sergei Skripal.
“Now Yevgeny Prigozhin has been added to that list, ending Putin’s humiliation.”
But Keir Giles, a Russia expert with the international affairs think tank Chatham House, urged caution about reports of Mr Prigozhin’s death.
According to the Associated Press, he said “multiple individuals have changed their name to Yevgeny Prigozhin, as part of his efforts to obfuscate his travels”.
As news of the crash was breaking, President Putin spoke at an event commemorating the Battle of Kursk, hailing the heroes of Russia’s war in Ukraine.