The Russian security service says that a 29-year-old man from Uzbekistan has been detained for the murder of senior general Igor Kirillov and his aide in Moscow.

Lt Gen Igor Kirillov, head of the Nuclear, Biological, Chemical (NBC) Defense Forces, was outside a residential block early Tuesday when an explosive device hidden in a scooter was detonated remotely.

Russia's security service said the unnamed suspect was recruited by Ukrainian intelligence, according to state media agencies.

The security service of Ukraine had already said that they were behind the murder, a source told the BBC Tuesday.

The Ukrainian source said Kirillov - Russia's former chemical weapons chief, was a "legitimate target" and said he had committed 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 public relations center of Russia's Federal Security Service (FSB) said on Wednesday that the 29-year-old arrested was "suspected of committing a terrorist act".

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

The FSB said the "confirmed" suspect received a reward of $100,000 and permission to move to the European Union in exchange for killing Kirillov.

He said that according to the instructions of Ukraine, 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 of the residential building where Kirillov lived, the FSB said.

He then rented a car to monitor Kirillov's residence and also installed a camera streaming live video from the site to his handlers in the Ukrainian city of Dnipro.

When they saw Kirillov coming out of the house, the suspect fired the bomb, the statement said.

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

In addition to being accused 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 said that Russia used chemical weapons more than 4,800 times under the General's direction.

Moscow denies this, and claims to have destroyed the last remnants of its large stockpile of chemical weapons in 2017.

Pictures from the scene outside Kirillov's apartment block in southeast Moscow on Tuesday showed the entrance badly damaged, with scorch marks on the walls and several windows blown out. Two body bags were also visible on the street.

Also on Wednesday, the Russian Foreign Ministry said that Russia will raise the murder of Kirillov at a meeting of the United Nations Security Council on Friday.

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