By Charles Haviland
BBC News, Colombo
Aid agencies that the needs of displaced people are immense
An international rights group has said many displaced Tamil people in camps in Sri Lanka have places to stay if they are allowed by the government to leave.
It has called for an end to the internment of 250,000 displaced people.
But the government continues to defend the confinement, saying that Tamil Tiger rebels "infiltrated" the camps at the end of the war last month.
Meanwhile one of several doctors who worked in the zone controlled by the rebels has been produced in court.
Dr T Satyamurthy is being detained on suspicion of collaborating with the Tigers in the final stages of the war which ended last month.
People streamed out of the warzone as the war drew to a close and many were subsequently kept in government-run camps.
Human Rights Watch says in a statement that a significant number of people in these camps have close relatives in the region with whom they could stay if they were let out.
The military has denied that shell attacks killed civilians
The government has prevented everyone in camps it controls between the ages of 10 and 60 from leaving, citing security reasons.
The lobby group said it was a "national disgrace" that all those detained were being treated "as if they were Tamil Tiger fighters".
It said international law prohibited arbitrary detention and unnecessary restrictions on freedom of movement.
In recent days government ministers have told the BBC they do not view all those in the camps as supporters of the Tigers - or LTTE - but said that there had been heavy infiltration by the former rebel group as the displaced people left the war zone.
They say that anyone espousing the ideals of the Tigers is violating Sri Lankan law and that they believe many refugees, including elderly ones, are still with the LTTE, "at least mentally".
They have admitted that the degree of support is hard to determine.
But they say strict security screening must continue and that people cannot leave the camps on a piecemeal basis.
Earlier this week more than 2,000 refugees did return from camps to their home villages in the north-west, having been screened.
On Tuesday the International Committee of the Red Cross (ICRC) said the needs of people in the camps were still "immense" and that those separated from their families desperately wanted to hear from them.
In a separate development, Dr Satyamurthy was produced before a magistrate's court in Colombo in accordance with the country's continuing state of emergency and identified before being sent back into custody pending further inquiries.
The government alleges that he and his companions, who were government health employees, supplied false information when they gave interviews to the foreign media from the war zone during the final months of the war.
In the interviews they said some of the shelling in the war zone came from the government side and had killed civilians.
Dr Satyamurthy said nothing during his brief court appearance.
The US says the doctors "helped save many lives" and has called them "heroic".