Colombo: Sri Lanka's health ministry is investigating three doctors detained by the military on accusations they gave false information about war zone casualties to the media, an official said on Saturday.

The doctors said they treated hundreds of badly wounded civilians in understaffed, makeshift hospitals in the north during the military's final offensive against the Tamil Tiger rebels. The physicians were among the few sources of information on those wounded and killed in the fighting, since most journalists were banned from the area.

Thurairaja Varatharajah, Thangamuttu Sathyamurthi and V. Shanmugarajah fled the war zone a week ago - just before the government routed the last rebels on the battlefield - and were immediately detained.

The health ministry has opened an investigation into accusations that the doctors - all government employees - provided incorrect and exaggerated details about civilian casualties and shortages of medicine and food, said Dharma Wanninayake, a ministry spokesman.

Once the inquiry is over, disciplinary action will be taken against the three, he said.

The detention of the doctors has raised international concerns, with human rights groups calling for their release.

The US State Department said the doctors "helped save many lives during the conflict and provided some of the only medical support available in the conflict area while caught between the (rebels) and Sri Lankan forces and facing extreme shortages of medical supplies."

"We urge the government to resolve the doctors' cases quickly and release them," the State Department said in a statement.