Russian state news agencies reported the explosive device – which killed 54-year-old Kirillov and his aide in Ryazansky Avenue – had an explosive force equivalent to 300g of TNT.

They added that bomb experts and specialist search dogs had inspected the surrounding area and no other explosives had been found.

Under UK sanctions, Kirillov was subject to an assets freeze and travel ban.

In May, the US accused Russia of deploying chemical weapons as a “method of warfare” in Ukraine, in violation of international laws banning their use.

State Department officials said Russia used the choking agent chloropicrin to win “battlefield gains” over Ukraine.

Ukrainian Col Artem Vlasiuk had previously said that more than 2,000 Ukrainian service members have been treated in hospital for chemical poisoning over the course of the war and three people have died.

The Kremlin rejected the accusations at the time, calling them “baseless”.

Kirillov served in different roles in Russia’s military associated with hazardous materials, including the Directorate of the Chief of the Radiation, Chemical and Biological Defence Troops.

According to the SBU, Russian forces drop chemical weapons on Ukrainian soldiers with drones.

He was appointed head of the NBC in 2017.