Thousands of Sri Lankans crammed into a squalid coastal strip along with retreating Tamil rebels face relentless shelling that has killed dozens of civilians in the past two days and left many scrounging for food to survive, witnesses said Thursday. Concern is growing for the trapped civilians as the Sri Lankan army seeks to deal a knockout blow to the Tamil Tiger rebels to end the island's 25-year civil war. The army, whose recent offensive has dismantled a de facto independent state carved out for Sri Lanka's ethnic minority Tamils, claims emergency supplies regularly reach the last rebel-held pocket in the northeast. But international aid agencies warn that stocks of food and medicines are so low that the area risks a humanitarian catastrophe. "It's been four days since my family has eaten," said Mary Jacinta Balachandran, 46, as she waited at the rebel pocket's only makeshift clinic.