US President Joe Biden has said American officials are trying to determine precisely how Wagner mercenary chief Yevgeny Prigozhin's plane was brought down in Russia, leaving no survivors.
Russia earlier scolded Mr Biden for expressing his lack of surprise that Prigozhin had been killed in a plane crash and cautioned that it was not appropriate for Washington to make such remarks.
Asked by reporters what brought the Wagner leader's plane down, President Biden said: "I'm not at liberty to speak to that precisely ... We're trying to nail down precisely, but I don't have anything to say."
Russian investigators said they have recovered flight recorders and ten bodies from the scene the crash.
An investigation is under way into what caused Wednesday's crash, which came exactly two months after Wagner's short-lived rebellion against Moscow's military leadership.
"In the course of initial investigative work, the bodies of 10 victims were found at the site of the plane crash," Russia's Investigative Committee said on social media.
"Molecular genetic analyses are being carried out to establish their identities," it said, adding that "flight recorders" were also recovered from the scene.
Since the crash, which also claimed the lives of some of Prigozhin's close entourage, many Western countries and Kremlin critics have speculated the Wagner chief could have been assassinated.
Earlier the Kremlin dismissed suggestions that it was involved in the death of the Wagner mercenary boss as an "absolute lie".
"There is a lot of speculation around the plane crash and the tragic death of the passengers, including Yevgeny Prigozhin," Kremlin spokesman Dmitry Peskov told reporters during a briefing.
"Of course, in the West, this speculation is being presented from a certain angle. All of this is an absolute lie," he insisted.
The denial of involvement comes as Vladimir Putin took steps to force members of all paramilitary groups to swear an oath to the Russian flag.
The presidential decree is aimed at "forming the spiritual and moral foundations for the defence of the Russian Federation" and applies to members of "volunteer formations", a term usually describing mercenary groups.
Details were published on the Russian president's website.
The UK says that, while there is not yet definitive proof Yevgeny Prigozhin was on board the plane which crashed with no survivors, it is "highly likely" that he is dead.
"The demise of Prigozhin would almost certainly have a deeply destabilising effect on the Wagner Group," the Ministry of Defence said in a intelligence update posted on social media platform X, formerly known as Twitter.
"His personal attributes of hyper-activity, exceptional audacity, a drive for results and extreme brutality permeated Wagner and are unlikely to be matched by any successor.
"Wagner's leadership vacuum would be compounded by the reports that founder and field commander Dimitry Utkin and logistics chief Valery Chekalov also died," the British ministry wrote.
Yesterday, Russian President Vladimir Putin sent his condolences to the family of Mr Prigozhin, breaking his silence after the mercenary leader's plane crashed with no survivors two months after he led a mutiny against army chiefs.
Mr Putin's comments, which suggested he harboured decidedly mixed feelings about Wagner's mercenary boss, were the most definitive yet on Mr Prigozhin's fate.
Before he spoke, the only official statement had come from the aviation authority which said Mr Prigozhin had been on board the downed plane.
Russian investigators have opened a probe into what happened, but have not yet said what they suspect caused the plane to suddenly fall from the sky northwest of Moscow on Wednesday evening.
Nor have they officially confirmed the identities of the ten bodies recovered from the wreckage.
The US Department of Defense said there was currently no information to suggest that a surface-to-air missile took down the plane.
The presumed death of Mr Prigozhin leaves Mr Putin stronger in the short term, removing a powerful figure who launched a mutiny in June against the army's leadership and threatened to make him look weak.
But it would also deprive Mr Putin of a forceful and astute player who had proved his utility to the Kremlin by sending his fighters into some of the bloodiest battles of the Ukraine war and by advancing Russian interests across Africa which are now likely to be re-organised.
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It remains to be seen too how Wagner fighters, some of whom have already spoken of betrayal and foul play, react.
Pledging a thorough investigation which he said would take time, Mr Putin said that "preliminary data" indicated that Mr Prigozhin and other Wagner employees had been on the downed plane. The passenger list suggests that Wagner's core leadership team were flying with him too and had also perished.
The Embraer Legacy 600 executive jet, which had been flying from Moscow to St Petersburg, crashed near the village of Kuzhenkino in the Tver region north of Moscow.
Part of the plane's tail and other fragments lay on the ground near a wooded area where forensic investigators had erected a tent.
The Baza news outlet, which has good sources among law enforcement agencies, reported that investigators were focusing on a theory that one or two bombs may have been planted onboard.
Residents of Kuzhenkino, the village near the crash site, said they had heard a bang and then saw the jet plummet to the ground. The plane showed no sign of a problem until a precipitous drop in its final 30 seconds, according to flight-tracking data.
Russian militants who fight on Ukraine's side and have carried out several attacks on Russian border regions urged the Wagner Group to avenge Mr Prigozhin's death and join their ranks.
Amid the absence of verified facts, some of his supporters have pointed the finger of blame at Russia, others at Ukraine, which marked its Independence Day yesterday.
Mr Putin said in June that Mr Prigozhin's the mutiny against the army, which saw Wagner fighters shoot down Russian military helicopters, could have tipped Russia into civil war.
The mercenary leader had also spent months criticising the conduct of Russia's war in Ukraine - which Moscow calls a "special military operation" - and had tried to topple Defence Minister Sergei Shoigu and Valery Gerasimov, chief of the General Staff.
The mutiny was ended by an apparent Kremlin deal which saw Mr Prigozhin agree to relocate to neighbouring Belarus. But he had appeared to move freely inside Russia.
Many Russians had wondered how he was able to get away with such brazen criticism without consequence.
Mr Prigozhin posted a video address on Monday which he suggested was made in Africa. He turned up at a Russia-Africa summit in St Petersburg in July.
