Igor Kirillov, the head of the military's chemical, biological and radiological weapons unit, was killed along with his deputy when the blast went off as the two men left a building in a residential area in southeastern Moscow early in the morning on Tuesday.

Kirillov, who was in October sanctioned by Britain over the alleged use of chemical weapons in Ukraine, is the most senior Russian military official to be killed in such a blast in Moscow since the start of Kremlin's offensive in Ukraine nearly three years ago.

"An unprecedented crime committed in Moscow", the Kommersant daily said on its website.

Russia's Investigative Committee said that Kirillov was killed after "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.

Kirillov, who had been in his post since 2017, oversaw the Russian military's Radiological, Chemical and Biological Defence unit.

The UK government in October slapped sanctions on Kirillov and his unit "for helping deploy these barbaric weapons", charges that Moscow has denied.

Britain and the United States have accused Russia of using the toxic agent chloropicrin against Ukrainian troops in violation of the Chemical Weapons Convention (CWC).

Chloropicrin is an oily liquid with a pungent odour known as a choking agent that was widely used during World War I as a form of tear gas.

The Organisation for the Prohibition of Chemical Weapons (OPCW) specifically prohibits its use.

Russia has said it no longer possesses a military chemical arsenal but the country faces pressure for more transparency over the alleged use of toxic weapons.

- Advancing troops -

In June, Ukraine accused Russia of increasing frontline attacks using prohibited hazardous chemicals and had registered more than 700 cases of their use the previous month.

Tuesday's blast came a day after Russian President Vladimir Putin said that his troops had the upper hand across the frontline in Ukraine.

In recent months Russia's army has advanced across eastern Ukraine at its fastest pace since the first weeks of the offensive, which Moscow launched in February 2022.

Both Moscow and Kyiv are seeking to improve their position on the battlefield before US President-elect Donald Trump comes to power in January. Trump has vowed to end the conflict.