Arbat battalion founder, Armen Sargsyan, has died in hospital, TASS news agency reports.
This comes after the leader of the pro-Russian paramilitary group was injured in an explosion in Moscow on Monday morning.
Sargsyan was severely injured following a blast in the entrance hall of a residential building in north-west Moscow, 12km from the Kremlin.
He was evacuated to a hospital by helicopter and placed in intensive care after the explosion.
However, the 46-year-old eventually succumbed to his injuries and gave up the ghost.
Sargsyan was accused by Kyiv of helping Russian forces in their war effort.
Meanwhile, in December, the Ukrainian security service SBU said Sargsyan was a suspect in “recruiting prisoners to fight in Ukraine”.
The SBU added that Sargsyan was part of the inner circle of fugitive former Ukrainian President Viktor Yanukovych.