Sri Lankan forces fired artillery shells into rebel-held territory and hit a makeshift hospital on Saturday, killing 64 civilians, according to government officials in the region and a Tamil-linked website.

Two shells hit the medical centre Saturday morning, Tamilnet.com reported, killing 23 and wounding 34. Later that morning, several more shells were fired at the hospital, killing 41 and injuring 53, according to the website.

The military has fighters of the Liberation Tigers of Tamil Eelam cornered in a tiny coastal area of northeastern Sri Lanka. An estimated 50,000 civilians are also believed to be trapped by fighting in the area.

A government health official said at least 64 patients and bystanders were killed in two artillery attacks that hit the hospital Saturday. Another 87 people were wounded, said the official, who declined to be identified by name because he was not authorized to speak to the media.

The BBC's Charles Haviland, reporting from Sri Lanka, said two doctors who work at the hospital corroborated Tamilnet's reports that 64 were killed in two separate incidents Saturday morning.

The hospital is inside rebel-held territory but is run by government doctors.

The Sri Lankan army denied the accusation, saying it has confined assaults to small-arms fire.

Pledge to stop using heavy weaponry

The government pledged Monday to immediately stop using air strikes and heavy weapons against the Tamil rebels to prevent further casualties among the thousands of civilians trapped in the war zone.

"We have not carried out any shelling, but we heard some loud explosions inside the no-fire zone and it could have been a misfire by the Tigers," military spokesman Udaya Nanayakkara told the Agence France-Presse news agency.

Neither account can be independently verified, as journalists are not allowed into the war zone. The International Committee of the Red Cross, which has limited access to the area, has not immediately commented on the reports.

Reports of chaos and suffering in the war zone have increased in recent weeks as the Sri Lankan military has pushed forward with a three-month offensive to destroy the separatist insurgency.

International pressure has grown for a ceasefire between the government forces and Tamil rebels to protect the trapped civilians. A UN report released last week put the number of noncombatants killed in the recent offensive at almost 6,500.

But the government has rejected calls for a ceasefire, saying such an action would allow LTTE forces to regroup and rearm.

The rebels have been fighting to create an independent homeland for ethnic minority Tamils, who they say have faced decades of marginalization by governments controlled by the ethnic Sinhalese majority.

With files from The Associated Press