The UN has said that at least 52 civilians have been killed in north-eastern Sri Lanka during fighting between government forces and Tamil Tiger rebels.
A UN spokesman said the only hospital in rebel-held territory was hit by cluster bombs.
The Tamil Tigers have said they will not lay down their arms until they have a guarantee of living with freedom and dignity and sovereignty.
However, Sri Lankan President Mahinda Rajapaksa said he was confident that the Tamil Tigers would be defeated within days.
In a national day address, Mr Rajapakse said the 'shadows of terrorism have almost been wiped out' with the last remnants of the Liberation Tigers of Tamil Eelam cornered in the jungle.
'I am confident that the Tigers will be completely defeated in a few days,' he said.
A military offensive over the past year has dismantled the Tigers' mini-state in northern Sri Lanka, where the rebels have lost 98% of the territory once under their control.
Clinton, Miliband urge no-fire period
But amid continuing fierce clashes, UN spokesman Gordon Weiss told wire services that at least 52 civilians were killed in one shelling attack yesterday evening.
'We don't know who is responsible or how many shells hit, but we have this report from our staff,' he said.
He added the region's only hospital was evacuated early today after 16 hours of shelling that included a cluster bomb attack.
As many as 250,000 civilians may be trapped in the combat zone, according to UN agencies.
Foreign governments, including the island's key backers, said the bloodshed must end.
US Secretary of State Hillary Clinton and her British counterpart David Miliband called yesterday for a temporary no-fire period to evacuate casualties and allow relief in.
'Both sides need to allow civilians and wounded to leave the conflict area and to grant access for humanitarian agencies,' they said after meeting in Washington.
The joint US-British statement came after the quartet of Sri Lanka's international backers - the US, EU, Japan and Norway - called on the rebels to negotiate terms of surrender to avoid a bloodbath.
The quartet, known as Co-Chairs, had backed Oslo-led peace moves and in April 2003 co-hosted a donor conference that raised $4.5bn in support of efforts to end ethnic bloodletting in the South Asian nation.
'There remains probably only a short period of time before the LTTE loses control of all areas in the north,' they said in a statement.
'The LTTE and the government should recognise that further loss of life of civilians and combatants will serve no cause,' they added.
There was no immediate reaction from the Tigers and the quartet said their efforts to persuade the LTTE to allow civilians to flee the fighting had failed.
Mrs Clinton and Mr Miliband insisted on the need for a political resolution to what is Asia's longest running ethnic conflict.
The Sri Lankan government - which pulled out of the Norwegian-brokered truce a year ago - has so far rejected the idea of a formal ceasefire, vowing to crush the Tigers, who have waged an armed campaign for a separate Tamil state since 1972.
It has also accused the rebels of using civilians as human shields.
Sri Lanka's army said yesterday that it had notched up further gains with the capture of an underground bunker complex believed to have been the home of the Tigers' leader, Velupillai Prabhakaran, as well as the rebels' last airstrip.
