Updated 9.05pm.

The Pentagon said Thursday it did not have information supporting theories that a surface-to-air missile was used to shoot down the aircraft of Wagner Group head Yevgeny Prigozhin.

The US military has "no information to suggest that there was a surface-to-air missile" involved in the crash, said Defence Department spokesman Pat Ryder, calling reports of a missile "inaccurate."

Ryder said he could not offer any information on what did cause the crash of the Wagner private aircraft northwest of Moscow on Wednesday, killing all 10 aboard.

But he said the US believed that Prigozhin was killed in the crash.

"Our assessment, based on a variety of factors, is that he was likely killed," said Ryder. 

Prigozhin's supporters claim the plane was brought down by an explosion.

Putin's 'condolences'

Russian President Vladimir Putin on Thursday expressed his "condolences" over the crash, describing Prigozhin as a man who made mistakes but "achieved results".

An investigation is currently underway into what caused the crash, which came exactly two months after Wagner's short-lived rebellion against Moscow's military leadership.

"First of all I want to express words of sincere condolences to the families of all the victims," Putin said in a televised meeting, calling the incident a "tragedy".

"I knew Prigozhin for a very long time, since the early 90s. He was a man of complicated fate, and he made serious mistakes in his life, but he achieved the right results," Putin added.

He said that an investigation had been launched into the crash, and that "it will take some time".

"It will be conducted in full and brought to a conclusion. There is no doubt about that," Putin said, in footage showing a meeting with the Russian-installed head of the Donetsk region Denis Pushilin.

The site where the plane carrying the Wagner group leadership crashed.

The circumstances of the crash, which claimed the lives of some of Prigozhin's close entourage, have prompted furious speculation about a possible assassination. 

The crash happened as a private plane with 10 people on board flew to St Petersburg. There were no survivors.