A high-ranking general in the Russian armed forces and his assistant have been killed in Moscow by Ukraine’s security service, a Ukrainian source has told the BBC.

Lt Gen Igor Kirillov, head of the Nuclear, Biological, Chemical Defence Forces (NBC), was outside a residential block early on Tuesday when a device hidden in a scooter was detonated remotely, Russia’s Investigative Committee said.

A source in Ukraine’s SBU security service claimed Kirillov was “a legitimate target” and alleging he had carried out war crimes.

On Monday, the SBU charged Kirillov in absentia, saying on Telegram that he was “responsible for the mass use of banned chemical weapons”. The Ukrainian government has not yet commented on the general’s death.

Pictures from the scene showed the badly damaged entrance to a building with scorch marks on the walls and a number of windows blown out. Two body bags could also be seen on the street.

The block was cordoned off on Tuesday morning as Russian investigators continued combing the area.

In October, the UK placed sanctions on Kirillov, saying he had overseen the use of chemical weapons in Ukraine and acted as a “significant mouthpiece for Kremlin disinformation”.

Ukraine’s SBU has claimed Russia used chemical weapons more than 4,800 times under the general’s leadership.

Moscow denies the allegations.

Russia’s Investigative Committee said it had “opened a criminal case into the murder of two servicemen”.

“Investigators, forensic experts and operational services are working at the scene,” it said.

“Investigative actions and operational search activities are being carried out aimed at establishing all the circumstances of the crime.”

Russian state news agencies reported the explosive device – which killed 54-year-old Kirillov and his aide in Ryazansky Avenue in the south-east of the city – 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.

Assassinations of senior officials have been carried out in Russia before, but attacks in Moscow are rare.

Residents living near the blast told the AFP news agency they initially thought the loud noise they heard had come from a 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.

Olga Bogomolova said she thought a container had fallen at the construction site but then realised “it was a very strong explosion”, saw “broken windows” and that it was something else.

People living in the area told the BBC of their deep sense of shock.

Even after three years of conflict, for many Muscovites, Russia’s war in Ukraine is something happening a long way away – something they only see on TV or on their phones.

The killing of a Russian general in Moscow is a sign that this war is very real and very close to home.

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.

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

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.

He was appointed head of the NBC in 2017.

Kirillov’s death comes less than a week after a prominent Russian weapons expert was shot dead near his home in Moscow.

Ukrainian media reported that the assassination of Mikhail Shatsky was carried out by Ukraine’s military intelligence service.