Armen Sargsyan, the founder of the pro-Russian paramilitary group Arbat Battalion, has passed away in hospital, according to TASS news agency.
This follows an explosion in Moscow on Monday morning that left him severely injured.
The blast occurred in the entrance hall of a residential building in north-west Moscow, approximately 12km from the Kremlin. Sargsyan, 46, was evacuated by helicopter and placed in intensive care, but ultimately succumbed to his injuries.
Sargsyan had been accused by Kyiv of aiding Russian forces in their war efforts. In December, the Ukrainian security service SBU identified him as a suspect in recruiting prisoners to fight in Ukraine.
The SBU also noted that Sargsyan was part of the inner circle of fugitive former Ukrainian President Viktor Yanukovych.
