MOSCOW (AFP): Russia's nuclear agency on Saturday said an explosion at an Arctic missile testing site had killed five of its staff after the military had put the toll at two.

The accident on Thursday happened during testing of a liquid propellant rocket engine at a missile test site in the far northern Arkhangelsk region.

In a statement, Rosatom said the accident killed five of its staff and injured three, who suffered burns and other injuries.

The statement came after authorities in a nearby city said the accident had caused a spike in radiation levels but the military had denied this.

Rosatom said its staff were providing engineering and technical support for the "isotope power source" of the missile engine.

The authorities have released few details of the accident at the Nyonoksa test site on the White Sea, used for testing missiles used in nuclear submarines and ships since the Soviet era.

The defence ministry initially said that six defence ministry employees and a developer were injured while two specialists died of their wounds.