Oleksandr Muzychko accusing Ukrainian prosecutors and police of plotting to kill him this month.
A leader of the Ukrainian ultranationalist group Right Sector and active participant in the Maidan street protests in Kiev has been shot dead in western Ukraine.
Oleksandr Muzychko, whom Russia had wanted on charges of committing war atrocities in Chechnya, was gunned down shortly before midnight Monday in the Ukrainian city of Rivne, the local Vse news website reported.
Ukrainian lawmaker Oleksandr Doniy said on his Facebook page that unknown assailants blocked off Muzychko's car, dragged him out of the vehicle, cuffed his hands behind his back, and shot him twice in the chest.
Vse and another Rivne website, ChaRivne, said that townspeople believed that Muzychko had been gunned down by a "Russian subversive group."
Crime scene photos published by Ukrainian news agencies showed a body in a torn-up jacket and shirt lying on the ground.
"Those who killed him made sure that he was not wearing a bulletproof vest and then shot him in the heart," Right Sector activist Yaroslav Hranitskiy said, ChaRivne reported.
Muzychko yelling obscenities and striking an official at the prosecutor's office in Rivne last month. Warning: 18+
Muzychko earlier this month accused the Ukrainian Prosecutor General's Office and police of planning to kill him or capture and hand him over to Russia.
"I am not afraid of death," he said in a YouTube video. He said his "friends, brothers, patriots" would "continue the battle."
Muzychko, a political embarrassment to the new Ukrainian government that came to power after the street protests, was vilified by Russia as a "fascist" for his ultranationalist views and violent outbursts.
In another YouTube video, Muzychko crudely assaulted employees at a prosecutor's office in Rivne last month, grabbing one man by his necktie and shouting obscenities. The video was subsequently circulated by the pro-Kremlin RT television channel.
Muzychko fought on the side of separatist rebels during the first Chechnya war of 1994-96. Russian Investigative Committee spokesman Vladimir Markin has said that Muzychko killed two dozen Russian servicemen in Chechnya.