At least nine people have been killed and three other are still missing after an explosion at a mine in north-west Russia, BBC reported Friday.

Workers were conducting controlled explosions at the mine when the blast occurred.

The mine is said to be owned by OAO Apatit, a major Russian company that produces apatite, a mineral commonly used in fertiliser.

"A large-scale blast was being prepared at the mine for which 55 tonnes of explosives had been laid," a source at the emergency situations ministry announced.

Many of Russia's mines have poor safety standards and have not been updated since the fall of communism.

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