Rebels in Indonesia's tsunami-devastated Aceh province accused the government of abandoning an informal cease-fire after the military said it had killed scores of suspected guerrillas to protect aid deliveries.

The rebels disputed the military's claim of killing 120 rebels in the past two weeks, saying only 20 of its fighters had died in skirmishes, while the remaining 100 were unarmed civilians.

The renewed hostilities in the nearly three-decade separatist conflict in Aceh called into question the security of relief efforts.

Gunfire was heard on Thursday near a camp housing tsunami survivors, causing many to run for cover. No one was hurt, and neither rebel fighters nor government troops could be seen during the sporadic firing of automatic weapons.

With thousands still missing, accurate tallies of the dead from the killer quake and waves that slammed into coastlines in Asia and Africa on Boxing Day have been almost impossible to obtain and have varied widely, from about 158,000 to 221,000.

But with as many as a million survivors still in need of food and shelter, international humanitarian groups warned that a US military decision to begin pulling back from relief operations could leave them unprepared to maintain the flow of aid.

"My gut feeling is that no, the civilian side isn't ready to take over," said Aine Fay, Indonesia director for the Irish aid group Concern. "The American military, the military hardware has been so useful. I'm a bit taken aback that they're thinking of withdrawing it already," she said.

More than 11,000 US Navy, Marines, Army, Air Force and Coast Guard personnel and 16 Navy ships are providing relief support in the tsunami's aftermath, according to the US Defence Department.

Since the operation began on January 1, they have delivered more than 8,600 tonnes of relief supplies to the affected region.

Indonesians living in aid camps were also worried about the withdrawal of American forces, whose helicopters have become the backbone of the relief effort.

"I want them to stay here 100 per cent. If they leave, there'll be no more food," said Mohamad Amin, a 50-year-old fisherman whose house was swept away by the waves. He is staying with 950 others in a filthy encampment in Aceh's provincial capital, Banda Aceh.

Amin said the Indonesian government would not be able to cope with the gargantuan task of rebuilding his province because of its financial difficulties. He said the Americans and other foreign volunteers should only leave when large numbers of refugees have been moved back to permanent settlements and given new jobs.

Indonesian military chief General Endriartono Sutarto said his troops had been forced to kill the suspected rebels because they were interfering in relief efforts in Aceh. "We cannot allow that to happen," he said. "We have to be able to guarantee that aid workers – foreigners and Indonesians – are safe to do their work."

Relief agencies have not reported any disruption to aid work from the rebels. They have agreed to Indonesian requirements to register and travel with military escorts.

Rebel spokesman Tengku Jamaica said most of those killed by the military were unarmed civilians. He denied the rebels were targeting aid convoys, and accused the military of abandoning the cease-fire.

In Sri Lanka, a Norwegian delegation arrived to try to further peace talks between that country's government and Tamil Tiger rebels.

A fragile cease-fire has been strained since the tsunami killed more than 30,000 Sri Lankans by accusations from each side that the other is obstructing deliveries in eastern Sri Lanka, where lines of control between the two sides are unclear.

Norwegian Foreign Minister Jan Petersen, in his role as peace broker, held "very constructive" talks with President Chandrika Kumaratunga, presidential spokesman Harim Peiris said.

Petersen and his team of envoys planned to meet reclusive insurgent leader Velupillai Prabhakaran in the rebel stronghold of Kilinochchi.

Nearly four weeks after the disaster, hundreds of delegates to a UN conference in Japan on disasters put the final touches on a pact backing the creation of a tsunami alert system to forewarn poor nations of cyclones, floods and other natural calamities.

But references in a planned final statement to global warming causing some natural disasters appeared likely to be removed after objections from the United States, Canada and Australia.