The Russian authorities said on Wednesday that they had detained a suspect in the killing of a senior military official, Lt. Gen. Igor Kirillov, in Moscow on the previous day.

The suspect, a 29-year-old citizen of Uzbekistan whose name was not released, was detained in a village outside of Moscow, a spokeswoman for Russia’s prosecutor’s office said.

The spokeswoman said the detainee had confessed that Ukrainian intelligence agencies recruited him to kill General Kirillov, who was in charge of the Russian military’s nuclear and chemical weapons protection forces.

The detainee traveled to Moscow and placed a bomb under a scooter near the general’s home, the spokeswoman added. An aide to the general was also killed when the bomb was detonated.

Speaking on condition of anonymity, an official with Ukraine’s security service, known as the S.B.U., said on Tuesday that Ukraine had been responsible for the killing.

This is a developing story.