The SBU press center said this in a statement seen by Ukrinform.
The detainee was acting on orders from Russia's Federal Security Service (FSB).
According to the case materials, to prepare the attack the suspect received coordinates of a cache from Russian handlers, retrieved an explosive device from it, and later bought thin fishing line at a local market to attach to the grenade's safety pin.
The SBU noted that the enemy planned to cause panic among local residents by detonating the explosive in a crowded area.
SBU officers uncovered the plot in advance and detained the would-be terrorist at night, at the site of the planned explosion.
The investigation found that the operation was carried out by a 62-year-old Kharkiv resident recruited by the occupiers through his wife, who lives in Moscow and works for the Russian intelligence service.
It was also documented that after setting up the tripwire, the agent planned to carry out another FSB task – to assemble a homemade explosive device using plastic explosives and a liquid detonator.
He was to plant the ready-made bomb in central Kharkiv for remote detonation by Russian intelligence officers during rush hour.
Read also: 'DPR' fighter planning to flee to EU detained in Volyn regionDuring searches at the suspect's residence, investigators seized a button phone used to set off explosives, a radio set, a smartphone, and a tablet containing evidence of his contacts with the enemy.
The SBU has charged the agent under Part 2 of Article 111 (high treason committed under martial law) and Part 1 of Article 14, Part 2 of Article 258 (preparation for a terrorist attack committed by a group of persons) of the Criminal Code of Ukraine.
The suspect is currently in custody and faces a possible life sentence with confiscation of property.
As reported earlier, SBU counterintelligence officers in Kharkiv previously detained another FSB agent who was preparing a homemade explosive device and planning to detonate it.