An Indonesian Red Cross medical team treating sick civilians in Aceh province was forced to withdraw after a gun battle between separatist rebels and troops, its leader said.

It was the first time since martial law was declared in Aceh nine months ago that the Indonesian Red Cross has attempted a medical mission to rugged countryside areas of the province, said Red Cross secretary general Iyang Sukandar.

"There was a firefight between the two sides. Thank God we weren't hurt," said Sukandar, who travelled from Jakarta to oversee the mission from the East Aceh capital of Langsa.

One of the 10 volunteers was left behind after the clash and Sukandar said his colleagues have not been able to give a clear explanation of what happened. "It is being handled by [Red Cross] headquarters," he said.

He said that unless their safety can be assured the Red Cross has no plans to try another medical mission. "We are ready to serve the people of the interior if it is truly safe for us," Sukandar told AFP by telephone.

Beginning Saturday afternoon the volunteers travelled from village to village treating people with malaria, fever and other ailments in the Peureulak and Idi Rayeuk areas of East Aceh, Sukandar said.

Asked whether the team treated rebels, he said, "We served the sick people. They were all in civilian clothes." Among the more than 20 people treated, none had gunshot wounds, he said.

The team travelled with guides from the rebel Free Aceh Movement (GAM) but had permission from local authorities including martial law authorities, Sukandar said. "This is official," he said.

But Aceh military spokesman Lieutenant Colonel Ditya Sudarsono said the Red Cross did not have permission from the martial law administrator.

Sukandar said that after the Monday morning firefight he immediately decided from his temporary base in Langsa that the team should be pulled out and troops brought nine of them to safety.

More than 1,300 guerrillas have been killed since the army launched an operation to crush GAM last May, according to the military. It says more than 2,000 others have been arrested or have surrendered.