A factory in Russia, described by its director as the world's biggest maker of strike drones, has been shown on the Russian army's TV channel with teenagers helping make kamikaze drones to attack Ukraine.

The footage, in a documentary film broadcast by the Zvezda channel on Sunday, showed hundreds of large black completed Geran-2 suicide drones in rows inside the secretive facility, which has been targeted by Ukrainian long-range drones.

Ukraine says Russia has used the Geran drones to terrorize and kill civilians in locations including the capital Kyiv, where residents often shelter in metro stations during attacks.