The United Nations called the killing of hundreds of ethnic Tamil civilians in a weekend artillery attack in northern Sri Lanka a "bloodbath" amid reports Monday that the war zone was heavily shelled for a second straight night. The initial artillery attack - which lasted from Saturday evening into Sunday morning - killed at least 378 civilians and wounded more than a thousand more, according to a health official inside rebel-controlled territory. A rebel-linked Web site blamed the attack on the government, while the military accused the beleaguered Tamil Tigers of briefly shelling their own territory to gain international sympathy and force a cease-fire. About 6 p.m. Sunday, a new round of shelling pounded the area, according to a government health official, who spoke on condition of anonymity because he was not authorized to speak to the media. The TamilNet Web site said many more civilians were killed in the second attack and that the death toll from the two days of violence was likely in the thousands.