Kyiv, Ukraine - Sources within Ukraine's security services have claimed responsibility for assassinating a senior Russian military official on Tuesday, and called it a "special operation."

High-ranking Russian general Igor Kirillov was killed on Tuesday when an explosive device attached to a scooter went off outside an apartment building in south-eastern Moscow.

Lieutenant General Kirillov was head of the Nuclear, Biological, Chemical Defense Forces (NBC) in Russia. On Monday, he was charged in absentia by Ukrainian authorities for war crimes involving the use of chemical weapons.

A source from within Ukraine's SBU security service told the AFP that the assassination was a "special operation" linked to the charges issued earlier this week.

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

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

Photos shared across Russian social media show the building's entrance severely damaged, with windows blown out and several body bags on the street.

Kirillov had sanctions imposed on him by the UK in October over the use of chemical and biological weapons, which are banned under international law.

"Russia’s cruel and inhumane tactics on the battlefield are abhorrent, and I will use the full arsenal of powers at my disposal to combat Russia’s malign activity," Foreign Secretary David Lammy said at the time.

The assassination of Kirillov is the highest-level target to be hit by Ukraine since the Biden administration allowed Kyiv to launch strikes on Russian territory in November.

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