A fire at a Soviet-era military base in Uzbekistan spread to an ammunition depot Thursday, setting off powerful explosions that killed three people and injured 21 others, the Uzbek government said.

A helicopter unit in Kagan, central Uzbekistan, caught fire at around 11 p.m. (1800GMT) Wednesday, a spokesman for the Emergency Situations Ministry said. Soldiers tried to put out the blaze, but could not keep it from reaching artillery shells, which began to explode, he said.

The Russia-based Ferghana.ru Web site, which covers Central Asia, quoted local residents as saying they heard explosions about three hours after the fire started. The explosions continued until morning with the biggest blasts shattering windows in Bukhara, 7 miles (12 kilometers) away.

The Soviet-era military base housed weapons left over from the Afghan War, which ended in 1989, the Web site said.

Reports differed over the extent of damage. The Web site said a train station and a hospital were destroyed, as well as more than 20 homes. An official from the Emergency Situations Ministry later denied that, the Russian RIA-Novosti news agency reported.

What caused the fire remains unclear.

The Russian news agency Interfax reported that Defense Minister Ruslan Mirzayev had arrived at the base but the threat of further explosions was hampering the investigation.

Uzbek state television and news agencies did not report the explosions for more than 12 hours after the fire broke out. Information is tightly controlled in the Central Asian nation.

Since its independence in 1991, Uzbekistan has been ruled by President Islam Karimov, a former Communist boss who has eliminated opposition and silenced critics.