Three people in St. Petersburg have been arrested on suspicion of plotting a terrorist attack on orders from Ukrainian intelligence, Russia’s Federal Security Service (FSB) said. The suspects allegedly planned to plant a homemade explosive device under the car of the head of a defense industry enterprise.

The suspects are a man and two women, born in 1993, 1994, and 2006. According to the FSB, two of them conducted surveillance and hid the device in a cemetery in St. Petersburg, where it was later retrieved by the man tasked with carrying out the attack.

After collecting the device, the man allegedly disguised himself as an elderly woman with a cane and set out to plant the bomb, but was arrested before he could do so. In video footage released by the FSB, officers are seen detaining a person in a long skirt and headscarf, followed by the arrest of a woman. Later scenes show a man with his face concealed saying that in July he had “joined a terrorist organization” and helped prepare the attack. Two women in the video also say they voluntarily joined a “terrorist organization.”

The FSB claims the suspects were acting on instructions from Ukrainian Defense Ministry’s Main Intelligence Directorate. They have been charged with preparing a terrorist attack and with the illegal possession of explosives.