Investigators have opened a probe into the crash, but have not officially confirmed the identities of the bodies recovered from the wreckage.
The Federal Security Service is Russia's primary security agency. It is Russia's successor to the KGB of the Soviet Union.
Yevgeny Prigozhin was a cruel warlord who did Russian President Vladimir Putin’s dirty work, but he also revealed the leader's weakness amid the stalled Ukraine offensive.
Putin described Prigozhin as a talented businessman whom he had known since the 1990s and said the investigation into the crash would take time.
Russian investigators opened a criminal probe but there has been no official word from Moscow on what may have caused Wednesday evening's crash.
Mirilashvili's legal team said that the defaming claims, made on social media, stem from the belief that the Georgian-born businessman is the owner of Channel 14.
There has been no official comment from the Kremlin or the Defense Ministry on the fate of Prigozhin but a Telegram channel linked to his Wagner mercenary group, Grey Zone, pronounced him dead.
Russian investigators opened a criminal probe. Some unnamed sources told Russian media they believed the plane had been shot down.
All ten people on board the aircraft died in the crash, according to the Russian Emergency Situations Ministry.
Wagner soldiers have also begun training with the Belarus army, and are being moved close to NATO's eastern flank to destabilize the military alliance.