"During the test of a liquid propellant jet engine, an explosion occurred and the equipment caught fire," the ministry said.

"As a result of the accident, six defence ministry employees and a developer were injured. Two specialists died of their wounds," it said, adding that radiation levels near the facility were "normal".

"There's no radioactive contamination," a spokeswoman for the Arkhangelsk region, where the base is situated, told AFP.

The accident is the second to hit the Russian military in less than a week, after a fire broke out in an ammunition depot in Siberia on Monday, causing huge explosions.

At least one person was killed and eight injured while thousands had to evacuated from their homes following the blaze at the depot in the Krasnoyarsk region.