The Indonesian military imposed sweeping restrictions on foreign aid workers in tsunami-hit Aceh, saying the move was needed to curtail a growing threat from separatist rebels.

Military chief General Endriartono Sutarto told reporters the armed forces would accompany and monitor aid groups on all missions outside the provincial capital of Banda Aceh.

Foreign aircraft and ships bringing supplies into Banda Aceh, the hub of the humanitarian effort following the December 26 disaster that killed more than 100,000 people in Aceh, will also no longer have unrestricted access.

Sutarto said a military officer will now be placed on board all foreign aircraft and ships and they would be given clearance to operate in the province for a maximum of 14 days.

Sutarto said the measures were needed to protect foreign aid workers from the Free Aceh Movement (GAM), which has been fighting for independence since 1976 – a rebellion which the military has violently suppressed.

The rebels' supreme commander Muzakir Manaf, in a statement, condemned the move and accused the government of "dispatching false news about our forces engaging in harassments of aid delivery". He said the rebels would guarantee the safety of all international volunteers.

Aid officials in Aceh and an analyst rejected Sutarto's assertions, saying there was no threat from rebels to the relief effort.

Sutarto said there had been one incident of a foreign medical officer being taken hostage for a short while, as well as others of rebels ambushing relief convoys. "GAM tried to stop food assistance, they robbed all the food and medicine there," Sutarto said, without giving any details about the alleged incidents.

Sutarto said in an interview published in the Jakarta Post on Tuesday that there was a danger the rebels may attack foreigners in Aceh. "That's why you see that a lot of our soldiers are still carrying weapons. That's one way that we provide protection to foreigners here," he said. "You know that killing a foreigner here will attract international attention, and they need it."

Sidney Jones, an expert from the International Crisis Group on Indonesian military and security affairs, told AFP that claims of a GAM threat were disingenuous.

"GAM has absolutely no interest in attacking foreign aid workers," Jones said. "What they want more than anything else is for an international presence to be there and stay there for a long time. It would go completely against the grain for them to mount attacks [against foreigners]."

Jones said the government's real motive for raising the security alert and restricting the movements of foreign aid workers was to reassert the military's control as it seeks to crush the rebellion. "I think the Indonesian military is very, very worried that two years of intensive military operations against the GAM is going to go to waste if there is an increased ability for people ... to move around the province," she said.

The Indonesian military imposed martial law in Aceh in May 2003, banning most foreign journalists and aid workers from the province, as it mounted a major new military offensive against the rebels.

The government lifted the restrictions on aid workers and journalists immediately after the disaster, although a state of emergency remains in place.

Mona Latzo, regional advocacy coordinator for international aid group Oxfam, said the organisation did not see GAM as a security risk. "We haven't seen any threat. We did have some trucks coming in [to Aceh] and they arrived safe and sound," Latzo said in Banda Aceh.

Despite the military claims of the rebel threat, Foreign Minister Hassan Wirayuda said the government was holding initial ceasefire talks with the insurgents. He said there had been a "gentleman's agreement" between the government and the rebels to halt fighting, although there had been no formal ceasefire pact.