Kirillov is the most senior Russian army official to be targeted on Russian territory, killed with his assistant when an explosive device attached to a scooter went off outside an apartment building in south-eastern Moscow.

"The liquidation of Lieutenant General Igor Kirillov, chief of the Russian Armed Forces' radiation, chemical and biological defence troops is a special operation by the SBU," the source said.

"Kirillov was a war criminal and an absolutely legitimate target, as he gave orders to use banned chemical weapons against the Ukrainian military," it said.

Kirillov was on Monday charged in absentia by Ukrainian authorities over alleged war crimes following an investigation by the SBU.

In October, he had been sanctioned by the UK over the suspected use of chemical weapons in Ukraine.

"Such an inglorious end awaits all those who kill Ukrainians. Retribution for war crimes is inevitable," the SBU source said.

It confirmed Kirillov was killed when "a scooter with explosives" detonated as he entered the building on Ryazansky Avenue in Moscow.