MOSCOW (AP) – A series of blasts from exploding shells rocked a Russian military test site on Tuesday, breaking windows and releasing giant clouds of smoke over the city of Orenburg near the Kazakhstan border. The emergency services said one military officer was hospitalized, but no other injuries were reported.

Military prosecutor Yevgeny Ivanov said on state television that the explosions were set off by a fire that may have been caused by someone smoking. The shells were being transported in crates in preparation for future disposal.

More than 4,000 tons of ammunition exploded, the Vesti television report said.

Military officials have opened a criminal investigation into the suspected mishandling of weapons at the Donguz test site, located about 40 kilometers (25 miles) from Orenburg.

Only two weeks ago, the head of a group carrying out the munitions disposal at Donguz was killed, Vesti reported.

Russian military equipment, which frequently dates back to the Soviet era, has exploded unexpectedly several times at test sites in recent years. Some of the accidents have been blamed on violations of safety procedures.