Ukraine kills Russian military's chemical weapons chief

The head of the Russian army's chemical weapons division was killed on Tuesday in a brazen attack in Moscow claimed by Kyiv -- the most senior military figure assassinated in Russia yet as the Kremlin's campaign in Ukraine drags on.

Igor Kirillov was killed along with his assistant when an explosive device attached to a scooter went off outside an apartment building in southeastern Moscow, Russian and Ukrainian officials said.

The attack took place in a residential area in the capital a day after President Vladimir Putin boasted of Russian troop successes in Ukraine, nearly three years on from the Kremlin's full-scale invasion of its pro-Western neighbour.

Kirillov, 54, was the head of the Russian army's chemical, biological and radiological weapons unit and was recently sanctioned by Britain over the alleged use of chemical weapons in Ukraine.

A source in Ukraine's SBU security service told AFP it was behind the early morning explosion in what it called a "special operation", calling Kirillov a "war criminal."

Russia's Investigative Committee said an "explosive device planted in a scooter parked near the entrance of a residential building was activated on the morning of December 17 on Ryazansky Avenue in Moscow".

The blast shattered several windows of the building and severely damaged the front door, according to an AFP reporter on the scene.

Russian authorities said they were probing the attack as "terrorism".

But the SBU source told AFP: "Kirillov was a war criminal and an absolutely legitimate target, as he gave orders to use banned chemical weapons against the Ukrainian military.

"Such an inglorious end awaits all those who kill Ukrainians. Retribution for war crimes is inevitable."

By Tuesday evening, the Kremlin had not commented on the attack, even after the authorities named Kirillov as the victim.

Ex-president Dmitry Medvedev said Russia must do everything it can to "destroy" Ukraine's political and military leadership who ordered the attack.

AFP was unable to verify video footage shared by an SBU source which showed a scooter exploding seconds after two men left a residential building.

Residents said they had initially assumed the loud noise they heard came from a nearby construction site.

Student Mikhail Mashkov, who lives in the building next door, said he was woken up by a "very loud explosion noise", thinking "something fell at the construction site", before looking outside