Banda Aceh – An Indonesian soldier serving in war-torn Aceh province opened fire on other troops at an army barracks, killing four and wounding one, an army spokesman said Tuesday.

The soldier, whose name wasn't released, has been arrested and is undergoing psychological tests, said Lt. Col. Ahmad Yani Basuki.

"He started shooting in all directions," said Basuki. "We suspect he was depressed as a result of the environment." The four victims were killed instantly in the shootings at the army base in the provincial capital Banda Aceh, he said. The condition of the injured man wasn't immediately known.

There are currently more than 50,000 soldiers and police stationed in Aceh, where they are fighting insurgents belonging to the Free Aceh Movement.

The rebels have been fighting since 1976 for an independent homeland in the oil- and gas-rich province on the northern tip of Sumatra island. At least 13,000 people have died in the conflict.