Doctors worked in extremely difficult conditions

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.

Under Investigation

Sri Lankan officials announced the arrest of the doctors on Monday.

In an interview with the BBC Tamil service on Tuesday, Foreign Secretary Palitha Kohona said the doctors are under investigation.

They are under investigation for breaches of the public service regulations which forbid public servents from speaking to the media - Palitha Kohona

"Breaches of the public service regulations which forbid public servents from speaking to the media. revealing information that is confidential to the public service etc." said the foreign secretary.

However, commander Sarath Fonseka told the BBC on Tuesday, that the whereabouts of the docters are unknown.

	Doctors are under investigation says the foreign secretary

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.

'Criminal acts'

They reported heavy bombardments and civilian casualties - some in the hospitals in which they were working - that were denied by the government.

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.

'The government will be held responsible'

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.

These are people who performed absolutely heroically in the last few weeks and months, and deserve every praise and care John Holmes, UK Humanitarian affairs chief

Physicians for Human Rights demanded that the doctors be released and given access to legal aid.

John Holmes

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."