[14] Following the Russian invasion of Ukraine, for direct participation in military actions against a sovereign state, Kirillov was added to the international sanctions list.

[18][19][20] According to the U.S. Department of State, Russia used chloropicrin under Kirillov's auspices, a choking agent widely used in World War I, as well as tear gas on the battlefield.

He died along with an assistant whose name was given by Russian authorities as Ilya Polikarpov (Илья Поликарпов)[22] as they were leaving a residential complex along the Ryazansky Prospekt area.

[26] A source in the Security Service of Ukraine stated that Kirillov "was a war criminal and a perfectly legitimate target" and warned that "such a disgraceful end awaits all those who kill Ukrainians.

"[20] According to Russian state media TASS, investigators found a hidden camera used to monitor Kirillov in a car-sharing vehicle nearby.

[27] Following the assassination, former president Dmitry Medvedev, who serves as deputy chairman of the Russian Security Council, pledged "inevitable retaliation" against Ukraine's military and political leadership.

Andrey Kartapolov, chairman of the Defense Committee of the State Duma, called him a "dignified Russian general" and "leader of his organization who was looked up to.

"[2] After the assassination, Vyacheslav Volodin, chairman of the State Duma, held a moment of silence for Kirillov, describing him as "not only a military leader, but first and foremost a scientist.