Lt. Gen. Igor Kirillov was killed by an explosive device that appears to have been hidden in a parked scooter and set off by remote control, Russian state-affiliated media TASS reported. The explosion also killed an aide accompanying him.
Kirillov was the head of Russia's radiation, chemical and biological protection troops. Sources told ABC News that the Security Service of Ukraine was behind the killing. Kirillov is the most senior Russian military official assassinated by Ukraine.
"Kirillov was a war criminal and an entirely legitimate target, as he issued orders to use prohibited chemical weapons against Ukrainian troops," an SBU source said. "Such an inglorious end awaits all those who kill Ukrainians. Retribution for war crimes is inevitable" the source said.
An SBU source provided ABC News with a video of the attack filmed from what appears to be a nearby vehicle.
"The footage shows Gen. Kirillov and his aide exiting a building, with the infamous scooter standing nearby," the source said. "The moment they enter the blast zone of the explosive device, the scooter is blown into the air, delivering a 'verdict' to the war criminal."
On Monday, the SBU charged Kirillov in absentia with war crimes for alleged orders approving chemical weapon use against Ukrainian troops.
Kirillov, the SBU said on Telegram, "is responsible for the mass use of banned chemical weapons" on the Ukrainian front lines.
"By order of Kirillov, more than 4,800 cases of the enemy's use of chemical munitions have been recorded since the beginning of the full-scale war," the SBU said.
Among the delivery methods, the SBU said, were grenades equipped with toxic substances like CS and CN irritants.
Kirillov was known for making allegations against Ukraine's foreign partners. The British Foreign Ministry in October described the general as a "significant mouthpiece for Kremlin disinformation, spreading lies to mask Russia's shameful and dangerous behavior."
Among Kirillov's claims were that the U.S. had built biological weapons laboratories in Ukraine, which was one of the many allegations used by the Kremlin to justify the 2022 full-scale invasion of the country. Kirillov also alleged that the U.S. helped Ukraine develop drone-launched "infected mosquitos."
Kirillov repeatedly suggested Kyiv was seeking nuclear escalation. He claimed that Ukraine was building a nuclear "dirty bomb" and this year suggested Kyiv's incursion into Russia's western Kursk region was intended to seize a nuclear power plant there.
Ivan Stupak, a former SBU official, told ABC News that Kirillov's killing represents a major success for Ukraine, the general being the highest ranking officer killed -- and "far beyond the front line."
"Scooters are so unnoticed in urban areas," Stupak added of the bomb's apparent delivery method.
ABC News' Oleksiy Pshemyskiy and Helena Skinner contributed to this report.