Sri Lankan troops killed 34 members of the separatist rebel group the Tamil Tigers Thursday during fierce fighting in the island's north in a drive to end a 25-year-old civil war, the military said. Troops collected the bodies of 31 rebels after intense clashes near Puthukkudiyiruppu, the last township held by the Tamil Tigers inside a tiny, shrinking territory, military spokesman Brig. Udaya Nanayakkara said in Colombo. [...] Tens of thousands of civilians are trapped in the war zone. The military says the rebels are using them as human shields in a desperate attempt to avoid defeat. But the Tigers say the people do not want to leave and have asked for their protection. [...] The United States has donated $15,000 worth of food aid to Sri Lanka, sufficient to feed 300,000 displaced people for four months, the U.S. Embassy in Colombo said in a statement. The aid represents 21 per cent of the total food aid called for this year by the World Food Program, the statement quoted USAID Mission Director Rebecca Cohn as saying.