MOSCOW: Russian President Vladimir Putin on Thursday expressed his "condolences" over a plane crash that killed Wagner chief Yevgeny Prigozhin, describing him as a man who made mistakes but "achieved results".

An investigation is underway into what caused Wednesday's 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 mentioned Prigozhin's work in Africa -- where Prigozhin claimed to be earlier in the week and where the Wagner group maintains a significant military presence.

Russian mercenary chief Yevgeny Prigozhin listed in plane crash with no survivors: authorities

"As far as I know, he just returned from Africa yesterday and met with some officials there," Putin said.

He said the investigation into the crash "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 circumstances of the crash, which claimed the lives of some of Prigozhin's close entourage, have prompted furious speculation about a possible assassination.

Prigozhin was branded a "traitor" by Putin after Wagner launched its rebellion in June, in what was seen as Putin's biggest challenge to authority since he came to power.

Among those killed in the crash was Dmitry Utkin, a shadowy figure who managed Wagner's operations and allegedly served in Russian military intelligence.

Putin said the Wagner members who died in the crash made a "significant contribution" to Moscow's offensive in Ukraine and shared a "common cause".

"We remember that, we know that, and we will not forget that," Putin said.