Russia’s Federal Security Service said on Thursday it had foiled several plots by Ukrainian intelligence services to kill high-ranking Russian officers and their families in Moscow using bombs disguised as power banks or document folders.

On December 17, Ukraine’s SBU intelligence service killed Lieutenant General Kirillov, chief of Russia’s Nuclear, Biological and Chemical Protection Troops, in Moscow outside his apartment building by detonating a bomb attached to an electric scooter.

An SBU source confirmed to Reuters that the Ukrainian intelligence agency had been behind the hit. Russia said the killing was a terrorist attack by Ukraine, with which it has been at war since February 2022, and vowed revenge.

“The Federal Security Service of the Russian Federation has prevented a series of assassination attempts on high-ranking military personnel of the Defence Ministry,” the FSB said.

“Four Russian citizens involved in the preparation of these attacks have been detained,” it said in a statement.

Ukraine’s SBU did not immediately respond to a Reuters request for comment.

The FSB, the main successor to the Soviet-era KGB, said that the Russian citizens had been recruited by the Ukrainian intelligence services.

One of the men retrieved a bomb disguised as a portable charger in Moscow that was to be attached with magnets to the car of one of the Defence Ministry's top officials, the FSB said.

Another Russian man was tasked with reconnaissance of senior Russian defence officials, it said, with one plot involving the delivery of a bomb disguised as a document folder.

“An explosive device disguised as a portable charger (power bank), with magnets attached, had to be placed under the official car of one of the senior leaders of the Russian Defence Ministry,” it said.

The exact date of the planned attacks was unclear though one of the suspects said he had retrieved a bomb on December 23, according to the FSB.

Russian state TV showed what it said was footage of some of the suspects who admitted to being recruited by Ukrainian intelligence for bombings against Russian defence ministry officials.

Moscow holds Ukraine responsible for a string of high-profile assassinations on its soil designed to weaken morale - and says the West is supporting a “terrorist regime” in Kyiv.

Ukraine, which says Russia’s war against it poses an existential threat to the Ukrainian state, has made clear it regards such targeted killings as a legitimate tool.

Darya Dugina, the 29-year-old daughter of a prominent Russian nationalist, was killed in August 2022 near Moscow. The New York Times reported that US intelligence agencies believe parts of the Ukrainian government authorised the killing.

US officials later admonished Ukrainian officials over the assassination, the Times said. Ukraine denied it killed Dugina.