Sri Lanka's Tamil Tiger rebels lashed out at the United Nations on Tuesday after it accused them of shooting civilians who try to escape the island's bloody ethnic conflict.
The UN said the Tigers have detained tens of thousands of non-combatants inside rebel-held territory and have "shot and sometimes killed" those crossing the battle lines to seek safety.
A front organisation for the rebels, who have been cornered in the jungle by government troops, countered the allegations by saying the United States had failed in its duty to protect innocent people.
The UN was "withdrawing even the remaining few local staff from the conflict zone (and) completely shedding its responsibility of caring for the civilians trapped here," said the Tamils Rehabilitation Organisation (TRO).
The statement, released on the pro-rebel website Tamilnet, came after the UN on Tuesday said that "a growing number of people trying to leave have been shot and sometimes killed."
The TRO, which is outlawed in several countries, including the United States, said the UN had levelled its harsh criticisms to hide "their own failures."
Tiger leaders have always denied charges that their fighters kill civilians or hold them as "human shields."
The UN also said the rebels had recruited 14-year-old child soldiers, and were detaining 15 UN staff and their dependents inside the conflict zone.
Government forces, who appear on the verge of crushing the rebels' 30-year campaign for an independent Tamil homeland, have said they are advancing with caution to avoid causing civilian deaths.
In Monday's statement, the UN urged both the Sri Lankan military and the Tigers to bring the war to a humane end so that civilians, including many children, would be spared.
The UN said it welcomed last week's declaration of a larger "safe zone" for civilians along the coastline, but noted there had been fighting even within that area.
"This fighting led to the deaths and injury to yet more civilians," it said. "The UN calls for the Sri Lankan forces and the LTTE (Liberation Tigers of Tamil Eelam) to refrain from fighting in areas of civilian concentration."
Tens of thousands of non-combatants in the rebel-held area were short of food, medicine and clean water, it added.
The International Committee of the Red Cross has warned that a "humanitarian catastrophe" was unfolding in the region and said hundreds of civilians have already been killed this year.
The UN, the United States and Britain have asked the Tigers to allow civilians to leave the conflict zone while urging the government in Colombo to declare a temporary truce. Both have rejected the calls.
On Saturday, the defence ministry accused the Tigers of a grenade attack that killed a woman and wounded 13 people who were trying to flee the shrinking area still under rebel control.