MOSCOW — A series of explosions has rocked a Russian military test site, releasing giant clouds of smoke over Orenburg near the Kazakhstan border and causing aftershocks.

Orenburg Gov. Yuri Berg wrote on his blog on Tuesday that the three explosions were caused by unplanned shell detonations. He says emergency services saw no potential harm to local residents.

The Emergency Situations Ministry says the shells exploded while being unloaded from a supply train.

Twitter users reported that police closed roads leaving Orenburg and evacuated residents from central buildings and nearby villages as a precautionary measure.

Russian military equipment, which frequently dates back to the Soviet era, has exploded unexpectedly several times at test sites in recent years.

President Vladimir Putin has pledged to overhaul and modernize the country's stagnant defense industry.