Thirteen people died in a blast during a disposal of expired military ammunition in Indonesia’s West Java on Monday, army officials told local media, the second incident involving expired ammunition in the country in little over a year.

Nine of the victims were civilians while four were military personnel, military spokesperson Kristomei Sianturi told Kompas TV, adding the military is investigating the cause of the incident.

Wahyu Yudhayana, a second army spokesperson, said in a televised address the blast happened when officers were finishing their disposal of the ammunition.

The investigation will include how civilians were allowed so close to the detonation site, he added.

The area where the blast happened is in a field where such detonations are routinely conducted, Kristomei said.

Local residents typically gather after the disposals to collect scrap materials left by the detonations, he said.

The area has been cleared to ensure safety in case of further explosions, he added.

Monday’s blast is the second incident involving Indonesian military ammunition in little over a year.

In March last year, a massive fire broke out at an Indonesian military depot storing expired ammunition near Jakarta, causing a series of explosions.