Russian law enforcement officers work in front of the damaged entrance to a residential building following a blast in Moscow on Monday

Agencies Moscow

A pro-Russian paramilitary leader from eastern Ukraine, Armen Sarkisyan, was killed on Monday when a bomb tore through parts of a luxury apartment block in Moscow, state news agency TASS and other Russian media reported. TASS called the bombing a well-planned assassination.

The bomb detonated just as Sarkisyan, accompanied by his bodyguards, entered the basement of the "Scarlet Sails" complex on the banks of the Moskva River just 12 km (7 miles) from the Kremlin, according to Russian media. One bodyguard was killed and three more injured, Kommersant newspaper said.

"The assassination attempt on Sarkisyan was carefully planned and was ordered. Investigators are currently identifying those who ordered the crime," TASS quoted a law enforcement official as saying. Baza, a Telegram channel with contacts in Russia's security services, published video showing major damage to the building's lobby.