At least 16 patients being treated at a makeshift hospital in the northern Sri Lankan war zone were killed by shelling, the Red Cross said, as the military accused rebel fighters of killing 19 other civilians fleeing the area.
The United Nations, meanwhile, said on Tuesday it was outraged by the "unnecessary" deaths of hundreds of people inside rebel territory and urged both sides to avoid fighting in civilian areas.
The government accuses the Tamil Tiger rebels of holding civilians hostage in the war zone to use as human shields against the military's offensive. The rebels deny the accusation.
International human rights groups say more than 200,000 civilians are believed trapped in the patch of territory still under rebel control.
Reports of civilian deaths have increased in recent weeks, and the Red Cross, the last major aid agency allowed to operate in rebel-held territory, said at least 16 patients were killed on Monday in shelling near a community center in the town of Putumattalan, where medical workers had evacuated many sick and wounded civilians.
"We are shocked that patients are not afforded the protection they are entitled to," said Paul Castella, head of the Sri Lankan delegation of the International Committee of the Red Cross. Castella did not say who was behind the shelling.
On Tuesday, local fishermen helped Red Cross workers ferry about 240 of the patients to a specially chartered boat anchored off Putumattalan to evacuate them from the war zone, said Sarasi Wijesinghe, a Red Cross spokeswoman.
The patients' injuries were making the operation difficult, she said.
"Most of them can't sit upright. They have to be lying down. A lot of care has to be exercised," she said. She said 140 other patients remained at the makeshift hospital, but the aid group hoped to evacuate them Wednesday.
The patients had fled the last functioning hospital in the war zone in Puthukkudiyiruppu last week after it came under repeated artillery barrages that killed several patients.
In recent days, the military has reported an increasing flow of civilians out of the war zone. Military spokesman Brig. Udaya Nanayakkara said the insurgents fired early on Tuesday on a group of more than 1,000 trying to escape the war zone in Udayarkattu. The attack killed 19 and wounded another 75, the military said.
Confirmation of the reported shooting was not possible because independent journalists are barred from the war zone. The rebels could not be reached for comment because communications to the north have largely been severed.