The exact nature of the assassination is still unclear, but multiple, unverified reports have emerged of an explosion in Tolstykh’s office. Insurgents have already blamed his death on Ukrainian operatives.

Thirty-six-year-old Mikhail Tolstykh, better known by his nom-de-guerre Givi, was reportedly killed on Wednesday morning.

A prominent pro-Russian guerilla commander has been assassinated in the self-proclaimed Donetsk People’s Republic, according to local officials.

Tolstykh was one of the most renowned — and reviled — field commanders in the bloody conflict between Ukraine and pro-Russian separatists. Tolstykh was a local Donetsk native and served in the Ukrainian army prior to the conflict as a tank commander.

In the spring of 2014, he joined the rebel forces and led a guerrilla battalion codenamed “Somali”. His unit took part in many of the fiercest battles in the Ukrainian conflict, including the siege of the Donetsk airport. Tolstykh was also accused of mistreating Ukrainian prisoners and was sanctioned by the European Union.

Tolstykh’s assassination follows a string of high-profile deaths in the ranks of separatist commanders, all of which Russia and separatist leadets have blamed on Ukrainian sabotage attacks. More likely theories focus on internal conflicts between separatists themselves and on the role of Moscow in eliminating insubordinate proxies.

Last October, Tolstykh’s comrade-in-arms, Russian insurgent leader Arseny Pavlov — also better known by his monicker “Motorola” — was killed by an explosion in an elevator in his home in Donetsk.