Artillery shells hit a makeshift hospital in Sri Lanka's northern war zone Saturday, killing at least 64 civilians, a government doctor and a rebel-linked Web site said, amid growing international pressure to safeguard thousands of civilians trapped in the area. The TamilNet Web site accused government forces of shelling the hospital at Mullivaaykkaal. 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. The hospital is inside rebel-held territory but is run by government doctors. Sri Lanka's defense ministry on Saturday rejected satellite imagery issued by the United Nations in support of allegations that security forces shelled a civilian area. The defense ministry said the allegations based on UN aerial images posted on the UNOSAT website and used on several foreign television channels had “no scientific validity” unless there was verification on the ground. “Conclusions drawn from the interpretations of these images have no scientific validity,” the ministry said, responding to reports the military had shelled an area the government itself had designated a no-fire zone. The pictures showed craters which were formed inside the zone between February 15 and April 19, the day before the army breached the Tigers' defenses and civilians started to pour out. “The imagery is fairly clear and shows the time, so anybody can study and compare them,” head of the mapping unit at UNOSAT, Einer Bjorge, said. He said the pattern of the craters would have required air power. Sri Lanka's top Tamil political force appealed Saturday for a way for cornered Tiger rebels to surrender to a third party and save tens of thousands of civilians trapped in the war zone. The Tamil United Liberation Front (TULF), a pro-government party, urged President Mahinda Rajapakse to name an international agency to which the Tamil Tiger guerrillas could hand over their weapons in exchange for an amnesty. The call came as government forces were poised for a final assault on a small patch of coastline into which the Liberation Tigers of Tamil Eelam (LTTE) are hemmed in the island's northeast. “I suggest that an international agency, acceptable to the government, be selected to visit (the rebel-held area of) Wanni and persuade the LTTE to allow the innocent people to go out freely,” TULF leader V Anandasangari said.