A Ukrainian separatist wanted by Kyiv was killed in a “carefully planned” explosion at a luxury apartment block in Moscow on Monday.

Armen Sarkisyan, 44, who founded the Arbat Battalion and headed a boxing federation in Russian-controlled Donetsk, died after a bomb detonated inside the building’s lobby.

The blast, which went off just as Sarkisyan entered with his bodyguards, had the power of one kilogram of TNT. It also killed a security guard and injured at least four others.

Local authorities have launched an investigation into the attack, though details about potential suspects remain unclear. No one has claimed responsibility for the blast.

“Sarkisian died in hospital after an assassination in Moscow,” the TASS news agency reported, after Russian media initially said he was seriously wounded in the blast.

Russian police earlier said one other person was killed in the “incident” at the complex in north-west Moscow, before Sarkisian’s death was confirmed.

The Kremlin said special services were working at the scene and declined to comment while “information was being clarified”.