"Due to an accidental blast in a unit ammunition store near Sihala, one soldier embraced (martyrdom) and three others were injured," a military spokesman said in a statement.
Earlier, witnesses and police officials had said at least three blasts ripped through the arms depot in Sihala, located about 20 km from the garrison city of Rawalpindi.
The military spokesman did not give details about the exact cause of the incident though TV news channels reported the blasts were caused by an electrical short circuit.
The blasts damaged a building and triggered a blaze that was later extinguished by army fire fighters. Police officials also told the media that the blasts were accidental and not an act of terrorism.
Army troops and policemen cordoned off the area and prevented people and media from approaching the arms depot.
Witnesses said they had seen several ambulances leaving the depot and going to a nearby military hospital.
Several government buildings, including a police training centre and facilities linked to Pakistan's nuclear programme, are located in the Sihala area which is heavily guarded.
Footage on television showed a plume of smoke rising into the sky over the arms depot. The footage also showed army fire brigade vehicles and ambulances driving into the depot.