Wagner boss Yevgeny Prigozhin is believed to have died in a plane crash in Russia.
Nine other people on board are also thought to have died in the crash, which took place at about 6.30pm local time (4.30pm UK time).
The jet crashed in the Tver region, north of Moscow. It was flying from the Russian capital to St Petersburg.
Prigozhin, the head of the notorious mercenary group who staged an attempted uprising in June, was on the plane, Russian aviation authorities said. The jet is thought to have belonged to him.
The Grey Zone, a media outlet linked to the Wagner Group, claimed the plane was shot down by a Russian air defence system.
Other outlets claimed two explosions were heard on board, with one Russian Telegram account saying the plane exploded into two pieces in mid-air.
Footage and images from the scene show the burning wreckage of a plane in a field.
One of Prigozhin’s closest allies, Dmitry Utkin, was also on board the plane.
A second plane belonging to Prigozhin is also said to be flying near Moscow.
The mercenary boss, who was exiled to Russian ally Belarus after the march on Moscow – released a video showing him speaking in camouflage and holding a rifle.
He is believed to have been in Africa, where the Wagner Group has operated in recent years.
It was the first video address Prigozhin had shared since the attempted uprising in June.