The Sri Lankan doctors had reported shelling in the conflict zone
International human rights groups have appealed for the release of three Sri Lankan doctors accused of giving false information to the media.
The doctors had been staffing makeshift hospitals on a shrinking patch of land where the Sri Lankan army isolated Tamil Tiger rebels.
With journalists banned from the conflict zone, they became an important source of news about the fighting.
Sri Lankan officials announced the arrest of the doctors on Monday.
One official told the Associated Press news agency that they had been detained for giving false information about civilian casualties to the media.
The doctors, who have been named as Thangamuttu Sathiyamoorthy, Thurairajah Varatharajah and V Shanmugarajah, treated some of the tens of thousands of civilians trapped in the conflict zone as the army closed in.
They reported heavy bombardments and civilian casualties - some in the hospitals in which they were working - that were denied by the government.
Sri Lanka has now declared victory in the government's 26-year conflict against the Tamil Tigers.
Amnesty International said it was concerned for the safety of the doctors and that it had received reports that Dr Sathiyamoorthy and Dr Shanmugarajah may be detained at the Terrorist Investigation Division (TID) in the capital, Colombo.
Dr Varatharajah was reported to be undergoing medical treatment after being seriously injured.
Reporters Without Borders urged the Sri Lankan government to show clemency.
"The government will be held responsible if the army's military victory is accompanied by such criminal acts of revenge against those have who have described the humanitarian tragedy," the group said.
Physicians for Human Rights demanded that the doctors be given released and given access to legal aid.
On Monday, UN humanitarian chief John Holmes said his organisation had not had any contact with the doctors.
"I would certainly urge the government to treat them properly," he said.
"These are people who performed absolutely heroically in the last few weeks and months, and deserve every praise and care."