Banda Aceh – A former separatist rebel was killed and a policeman wounded in an attack witnessed by members of a foreign peace monitoring mission in Indonesia's Aceh province, police said Tuesday.

The ex-Free Aceh Movement (GAM) rebel, aged 32, was killed during a shootout Monday between Indonesian soldiers and unknown gunmen in North Aceh, police spokesman Jodi Heriyadi told AFP.

The skirmish, which also wounded a policeman and another civilian, occurred at dusk while members of the Aceh Monitoring Mission (AMM) and soldiers were investigating the arrest of a civilian by local military in the area.

The civilian had been arrested in front of a military post for speeding on a motorcycle and allegedly carrying marijuana, Heriyadi said.

He said AMM officials, military officers and several former GAM members were being briefed on the arrest along with several civilians when gunmen fired upon the group. Soldiers manning the post retaliated by shooting toward the gunmen.

One of the ex-GAM members was killed, while the policeman who was escorting the AMM officials, and a civilian in the group was wounded, Heriyadi told AFP. "This case is still being investigated by the AMM and Indonesian authorities," he said.

The AMM confirmed the attack. "This serious incident will be further investigated... with a particular view to clarifying the facts and ascertaining that the law has been respected," the AMM head of mission Pieter Feith said in a statement.

He said the AMM would look into whether the armed forces had interfered in law enforcement and whether excessive force was used. "AMM is particularly concerned that its monitors were placed in danger in the course of their duties," Feith added.

The Indonesian government and GAM signed an historic peace pact on August 15, aimed at ending 29 years of conflict which has left around 15,000 people dead – mostly civilians.

The AMM is due to wrap up its mission in September. Nearly 200 monitors were initially stationed in Aceh after the pact was signed, but about 100 left in March when the mission was scaled back.