Military spokesman Brig. Udaya Nanayakkara denied the accusation, saying soldiers were only using small arms as they pushed forward to seize the remaining territory held by separatist Tamil Tigers along a small coastal strip in the island's northeast.
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.
TamilNet said the shells struck on both Friday and Saturday. It gave the same casualty toll as the health official.
The hospital is inside rebel-held territory but is run by government doctors.
The artillery attacks came amid growing international concern over the fate of the estimated 50,000 civilians trapped in the war zone, following a U.N. report that nearly 6,500 civilians were killed in the last three months.
International pressure has grown for a cease-fire between the government forces and Tamil rebels to protect the trapped civilians.
The government has rejected calls for a cease-fire, saying its troops are on the verge of ending the quarter-century civil war. They instead promised on Monday to stop using artillery attacks, airstrikes and other heavy weapons to ensure the safety of the trapped civilians.
But pro-rebel reports say government forces continue to shell the area.
The government and rights groups, meanwhile, accuse the rebels of holding the civilians as human shields.
The various claims are difficult to verify because most journalists and independent observers are barred from the conflict zone.