The factory, which is located in the region of Bashkortostan, produces weapons and ammunition used in the war against Ukraine. According to the region's governor, "the factory performs an important state task".
On social media, he writes that a violent explosion was heard from the area and that three women have been killed.
An additional five people have been taken to hospital.
The cause of the explosion is unknown.
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Ukraine has carried out drone attacks against an oil refinery in the area earlier in the autumn.
