A mortar shell struck the only functioning medical facility in Sri Lanka's northern civil war zone Tuesday, killing 49 patients and bystanders and wounding more than 50 others, separatist fighters and a health worker in the area said.

The attack came after a weekend of heavy shelling that killed hundreds of civilians in the area. The military has denied accusations that it was still shelling the tiny coastal strip still under insurgents' control, which is packed with an estimated 50,000 civilians.

Separatist spokesman Seevaratnam Puleedevan said a shell hit the hospital Tuesday morning. "They are still counting the dead bodies," he said.

A health worker at the makeshift hospital confirmed the attack, saying one mortar shell landed in the admissions ward that had been set up in a temporary shelter about 7:30 a.m., killing patients and bystanders and sending dozens fleeing for their lives.

A hospital administrator was among those killed and another 56 people were wounded, the staffer said, speaking on condition of anonymity because he was not authorized to speak to the media.

Shelling was still going on hours after the attack, but the hospital was not again hit, the worker said.

Puleedevan said civilians were fleeing in all directions inside the tiny war zone seeking safety.

"There's no place to seek shelter or protect themselves," he said.

He called on the international community to force the government to stop its offensive against the militants.

Sri Lanka's 25-year-old civil war has pitted Tamils, an ethnic minority in the country, against the Sinhalese-controlled government. The conflict has killed an estimated 70,000 people.

Accurate reporting on the war is difficult because journalists are banned from conflict zones, while most foreign reporters are barred from entering the country in the first place.