Agencies in Jakarta and Banda Aceh – Troops in Aceh will shoot on sight anyone found lowering the national flag tomorrow, the 23rd anniversary of the region's separatist movement, the province's military chief was quoted as saying yesterday.

Thousands have fled the province in northern Sumatra anticipating violence on the anniversary of the Islamic Aceh Merdeka or Free Aceh movement, which has recently stepped up its demands for independence.

Jakarta's Kompas daily quoted Aceh military chief Colonel Syarifuddin Tippe as saying he had ordered his troops "to shoot anyone found lowering the red-and-white [Indonesian] flag".

Provincial police chief Brigadier-General Kasman Bahrumsyah said Aceh Merdeka could hoist their flags but also warned of "stern measures" if they forced residents to do so.

Military spokesman Major-General Sudradjat renewed a call for the Government to declare martial law. "Facing the rebels, we will be careful unless they provoke us to act violently," he said.

Free Aceh Movement supporters are planning large celebrations to mark the anniversary. The group has said the rallies will be peaceful.

Movement commander Teuku Abdullah Syafei had appealed to residents not to raise the flag tomorrow, the Serambi daily said. It also said 26 people trying to trigger unrest, including five military officers, had been caught.

In the latest violence, a battle between troops and rebels in the village of Peuriba left a soldier and two civilians dead yesterday, said Lieutenant-Colonel Widhagdo, the head of the local military.

But witnesses said the two civilians were killed when soldiers opened fire on a crowded market after one of their officers was killed in a rebel ambush. Four civilians were wounded, they said. In a separate incident, the bodies of two civilians were found in east Aceh, police said.

Human rights groups claim more than 5,000 people in Aceh have been killed or have disappeared at the hands of the security forces since 1989.

A car carrying two foreign journalists was caught in crossfire between troops and rebels in Lammo, west Aceh, on Tuesday, Kompas reported yesterday. The journalists, a Japanese and an American, were not injured, it said.