A top Russian general accused by Ukraine of being responsible for the use of chemical weapons against Ukrainian troops was assassinated in Moscow by Ukraine's SBU intelligence service on Tuesday morning in the most high-profile killing of its kind.

Lieutenant General Igor Kirillov, who was chief of Russia's Nuclear, Biological and Chemical Protection Troops, was killed outside an apartment building along with his assistant when a bomb hidden in an electric scooter went off, Russia's Investigative Committee, which probes serious crimes, said.

An SBU source confirmed to Reuters that the Ukrainian intelligence agency had been behind the hit. "The liquidation of the chief of the radiation and chemical protection troops of the Russian Federation is the work of the SBU," the source said.

The source said that a scooter containing explosives was detonated, killing both Kirillov and his aide, as they stepped into the entrance of a house on Ryazansky Prospekt in Moscow.

Kirillov, 54, is the most senior Russian military officer to be assassinated inside Russia by Ukraine and his murder is likely to prompt the Russian authorities to review security protocols for the army's top brass and to find a way to avenge his killing.

Former president Dmitry Medvedev, now a senior Russian security official, was cited by the state RIA news agency as saying that Ukraine's military and political leadership now faced imminent revenge for Kirillov's murder.

Moscow holds Ukraine responsible for a string of high-profile assassinations on its soil designed to weaken morale and punish those Kyiv regards guilty of war crimes. Ukraine, which says Russia's war against it poses an existential threat to the Ukrainian state, has made clear it regards such targeted killings as a legitimate tool.

Reuters photographs and video from the scene showed a shattered entrance to an apartment building with bomb-blackened bricks and the doors hanging off their hinges and what looked like two bodies lying beneath black plastic sheets on the snow.

Investigators said they had opened a criminal case into the murder of two servicemen. Law enforcement sources told Russian media a terrorism case was likely to be opened.