Russia’s FSB security agency has announced the arrest of a Ukrainian citizen, who was allegedly seeking to plant a powerful improvised explosive device inside a transport terminal in the city of Bryansk.

According to Wednesday’s report, the male in his mid-50s travelled to Russia from Ukraine via Estonia. Once in Russia, he recovered the components for an IED from a stash pre-prepared by the Ukrainian special services, the statement claimed.

He later allegedly assembled the bomb at a rented apartment, with an intelligence agent specializing in explosives giving instructions on how to build and test it. The device was adapted from an anti-tank missile warhead and had a yield equivalent to 3 kg of TNT, according to the description.

The FSB said the suspect observed the warehouses of a logistical company in Bryansk, where he wanted to plant the device, before being arrested by Russian law enforcement. Bryansk Region shares a border with Ukraine.

Russian law enforcement has released footage, purportedly showing the moment the suspect was apprehended. The video includes the unpacking of the alleged bomb.