An explosion at a Russian factory in the Urals producing ammunition and weapons for the military has left at least 10 people dead, reports say.


Witnesses described seeing explosions and a fireball at the Plastmass military plant in Kopeisk, near the city of Chelyabinsk.


Regional governor Alexei Teksler did not specify which factory had been hit but he confirmed the death toll. Tass news agency reported that 18 other people had been injured.


Authorities have not disclosed what caused the blast but Teksler emphasized that there is no talk of a UAV (drone) attack.


A day of mourning has been announced, and investigators say they have opened a criminal inquiry into the blast.


Teksler mentioned that the fire in Kopeisk had been extinguished.