Footage shows one of Vladimir Putin's war factories erupting into flames after a suspected Ukrainian drone exploded.
A fireball burst as an unmanned aerial vehicle (UAV) hit the plant in Yelabuga, Russia.
It is believed that the plant was where Iranian killer drones were being assembled.
Three strikes were reported which left several people wounded.
Footage shows one of Vladimir Putin's war factories erupting into flames after a suspected Ukrainian drone exploded
Reuters
It is not clear whether the attack was carried out by a piloted small plane on a suicide mission or whether the aircraft was flying on autopilot.
Kremlin-loyal news webiste Readovka reported: "It is too early to conclude whether the suicide pilot was alive at the wheel or whether the aircraft was controlled by an autopilot.
"In favour of the latter is the fact that how straight and clear the A-22 went to the target - such a result could not be achieved even by Japanese kamikazes, so, apparently, we are dealing with a new kind of long-range kamikaze drones based on light-engine aircraft."
Others suggested the attack was by a UJ-22 airborne drone.
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Head of Tatarstan region Rustam Minnikhanov said: "This morning, the enterprises of the republic in Elabuga and Nizhnekamsk were attacked by unmanned aerial vehicles.
"There was no serious destruction, the technological process of the enterprises was not disrupted.
"There are victims as a result of the destruction of the premises. They are being provided with all the necessary assistance."
As the plant is located at least 660 miles from the closest Ukrainian territory, there is speculation that the drone launched from Russia, or Kazakhstan.
It is believed that the plant was where Iranian killer drones were being assembled
Reuters
The Taneco oil plant in Nizhnekamsk was also hit early today.
It is the latest oil refinery in Russia to be hit by Ukraine.
The bombardment of oil refineries in Russia has sparked concern for rising world oil prices.