The bodies of those individuals who died in the August plane crash that killed Wagner Group leader Yevgeny Prigozhin contained "fragments of hand grenades," according to the Russian Investigative Committee tapped to look into the crash.

The plane crash on Aug. 23 in the Tver region of Russia killed 10 people, including Prigozhin and Wagner Group co-founder Dmitry Utkin.

"The head of the Investigative Committee reported just the other day that the bodies of those killed in the plane crash were found fragments of hand grenades," President Vladimir Putin said at the Valdai Club meeting in Sochi, Russia on Thursday. "There was no external impact on the plane. This is already an established fact. The fact is the result of an examination conducted by the Investigative Committee of the Russian Federation."

Prigozhin rose to become a powerful international paramilitary leader and was a former close ally of Putin.

The crash may have been caused by an explosion on board the plane, perhaps by a well-placed bomb, U.S. officials told ABC News in August, describing their findings from an initial investigation.

The death of Prigozhin came exactly two months after he led a daylong mutiny against Moscow.

Wagner Group forces, which had been fighting in Ukraine, turned from their headquarters in Rostov-on-Don and marched toward the capital in the evening on June 23. Within a day, they had turned back.

Several Wagner fighters have signed contracts with the Russian Ministry of Defense and will take part in hostilities, Putin said Thursday.

In late August, White House press secretary Karine Jean-Pierre laid out the Kremlin's "long history" of "killing its opponents," before telling reporters it's "pretty evident what happened here."

The Kremlin has called it "sheer lies" that they were involved in downing the plane.

ABC News' Meredith Deliso and Tanya Stukalova contributed to this report.