Russia's security service said Wednesday that it has detained a suspect in the killing of a senior general in Moscow.

The suspect was described as an Uzbek citizen recruited by Ukrainian intelligence services.

Russia's Federal Security Service, or FSB, didn't name the suspect, but said he was born in 1995. According to a statement by the FSB, the suspect said himself that he was recruited by Ukrainian special services.

 Lt.-Gen. Igor Kirillov was killed Tuesday by a bomb hidden in a scooter outside his apartment building in Moscow, a day after Ukraine's security service leveled criminal charges against him. His assistant also died in the attack. A Ukrainian official said the service carried out the attack.

The FSB said the suspect had been promised a reward of $100,000 US and permission to move to a European Union country in exchange for killing Kirillov.

WATCH | Kirillov was under sanctions from many countries, including Canada:

Moscow explosion kills top Russian general

Russia has vowed revenge after the early morning assassination of a top general in a residential Moscow neighbourhood. Ukraine's intelligence service has claimed responsibility.

The agency stated that, acting on instructions from Ukraine, the suspect travelled to Moscow, where he picked up a homemade explosive device. He then placed the device on an electric scooter and parked it at the entrance to the residential building where Kirillov lived.

Explosion livestreamed

The suspect then rented a car to monitor the location and set up a camera that livestreamed footage from the scene to his handlers in the central Ukrainian city of Dnipro. Once Kirillov was seen leaving the building, the suspect detonated the bomb.

According to the FSB's statement, the suspect faces "a sentence of up to life imprisonment."

Kirillov, 54, was the chief of the military's nuclear, biological and chemical protection forces and was under sanctions from several countries, including the U.K. and Canada, for his actions in Moscow's military operation in Ukraine. On Monday, Ukraine's Security Service, or SBU, opened a criminal investigation against him, accusing him of directing the use of banned chemical weapons.

Russia has denied using any chemical weapons in Ukraine and, in turn, has accused Kyiv of using toxic agents in combat.

Kirillov, who took his current job in 2017, was one of the most high-profile figures to level those accusations. He held numerous briefings to accuse the Ukrainian military of using toxic agents and planning to launch attacks with radioactive substances — claims that Ukraine and its Western allies rejected as propaganda.

The bomb used in Tuesday's attack was triggered remotely, according to Russian news reports. Images from the scene showed shattered windows and scorched brickwork.

Russia's top state investigative agency said it's looking into Kirillov's death as a case of terrorism, and officials in Moscow vowed to punish Ukraine.