Russian security services say a 29-year-old man from Uzbekistan has been detained in connection with the killings of top general Igor Kirillov and his aides in Moscow.

Earlier on Tuesday, an explosive device hidden in a motorcycle was detonated remotely outside a residential complex by Lieutenant General Igor Kirillov, head of the radiation, chemical and biological protection force.

Russian security services said the unnamed suspect was recruited by Ukrainian intelligence services, state media agencies reported.

Ukrainian security services have claimed to be behind the killings A source told the BBC Tuesday.

Ukrainian sources say Russia’s chemical weapons chief Kirillov is a “legitimate target” and claim he committed war crimes.

On Monday, the day before the murder, Ukraine charged Kirillov, 54, in absentia, saying he was “responsible for the large-scale use of banned chemical weapons.” Russia denies the accusations.

The Public Relations Center of Russia’s Federal Security Service (FSB) said on Wednesday that the 29-year-old man detained was “suspected of committing terrorist acts.”

“During interrogation, he explained that he had been recruited by Ukrainian special forces,” a statement said.

The FSB said the suspect was “guaranteed” a $100,000 reward and permission to emigrate to the EU in exchange for killing Kirillov.

On instructions from Ukraine, he arrived in Moscow and received a homemade explosive device, the statement added.

Russia’s Federal Security Service said he placed the explosive device on an electric scooter and parked it at the entrance to the residential building where Kirillov lived.

He then rented a car to monitor Kirillov’s residence and installed a camera that transmitted live video from the scene to his managers in the Ukrainian city of Dnipro.

The suspects detonated the bomb when they saw Kirillov coming out of the house, the statement said.

Kirillov is believed to be the most senior military figure to be assassinated on Russian soil since Russia invaded Ukraine nearly three years ago.

In addition to being charged by Ukraine, the 54-year-old man has previously been charged with Sanctioned by UK for suspected use of chemical weapons in Ukraine.

Ukraine’s SBU security service claims that under the general’s leadership, Russia used chemical weapons more than 4,800 times.

Moscow denies this and It said it destroyed the last remaining portion of its vast chemical weapons stockpile in 2017.

Photos taken on Tuesday outside an apartment building in Kirillov, southeast of Moscow, showed heavily damaged entrances, scorch marks on the walls and several blown-out windows. Two body bags could also be seen on the street.

Also on Wednesday, the Russian Foreign Ministry said Russia would raise the Kirillov assassination at a U.N. Security Council meeting on Friday.

Russian officials vowed to find and punish those involved in the killings.