Sri Lanka ? A mortar shell slammed into a crowd of wounded civilians waiting for treatment at the only medical facility left in Sri Lanka’s war zone Tuesday, killing 49 people in the third day of intense shelling in the area, health officials said.

The Tamil Tiger rebels blamed the government for the attack — the second deadly strike on the hospital this month — and called on the international community to push for an immediate cease-fire.

Sri Lankan officials denied responsibility, saying they had ceased using artillery and mortars weeks ago. But the U.N. humanitarian chief said there was evidence the government was still using heavy weapons, despite the estimated 50,000 civilians stuck in the tiny coastal strip still under rebel control.