Russia’s security service says a 29-year-old man from Uzbekistan has been detained over the killing of senior general Igor Kirillov and his assistant in Moscow.

Lt Gen Igor Kirillov, head of the Radiation, Chemical and Biological Protection Forces, was outside a residential block early on Tuesday when an explosive device hidden in a scooter was detonated remotely.

The Russian security service said the unnamed suspect was recruited by Ukrainian intelligence, according to state media agencies.

Ukraine’s security service had already claimed it was behind the killing, a source told the BBC on Tuesday.

The Ukrainian source said Kirillov – who was Russia’s chemical weapons chief – was “a legitimate target” and alleged he had carried out war crimes.

On Monday, the day before the killing, Ukraine charged Kirillov, 54, in absentia, saying he was “responsible for the mass use of banned chemical weapons”. Russia denies the allegations.

The Russian Federal Security Service’s (FSB) public relations centre said on Wednesday the detained 29-year-old was “suspected of committing a terrorist act”.

A statement said that during “interrogation he explained that he was recruited by the Ukrainian special services”.

In a video published by the FSB, the purported suspect appears to say he was offered a reward of $100,000 and permission to move to the European Union in exchange for killing Kirillov.

It added that on Ukraine’s instructions, he arrived in Moscow and received a homemade explosive device.

He placed the explosive device on an electric scooter, which he parked at the entrance to the residential building where Kirillov lived, the FSB said.

He then rented a car to monitor Kirillov’s residence and installed a camera on the dashboard which livestreamed a video feed to handlers in the Ukrainian city of Dnipro, the statement added.

When they saw Kirillov emerge from the house, the suspect was told to press the button and detonate the bomb, the FSB said.

Kirillov is thought to be the most senior military figure assassinated inside Russia since the country invaded Ukraine nearly three years ago.

Alongside being charged by Ukraine, the 54-year-old had previously been sanctioned by the UK over the alleged use of chemical weapons in Ukraine.

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

Moscow denies this, and says it destroyed the last remainder of its vast chemical weapons stockpile in 2017.

Pictures from the scene outside Kirillov’s apartment block in south-eastern Moscow on Tuesday showed the badly damaged entrance, with scorch marks on the walls and a number of windows blown out. Two body bags could also be seen on the street.

Also on Wednesday, the Russian Foreign Ministry said Russia would raise Kirillov’s assassination at the meeting of the United Nations Security Council on Friday.

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