Moscow, Russia - 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 currently 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.

Joe Biden Biden "looking into" freeing Leonard Peltier as demands for clemency grow

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