Navi Pillay, the U.N. high commissioner for human rights, said some actions taken by the military and the Liberation Tigers of Tamil Eelam could violate international human rights and humanitarian laws, the United Nations said in a news release.
"We need to know more about what is going on but we know enough to be sure that the situation is absolutely desperate," Pillay said. "The world today is ever-sensitive about such acts that could amount to war crimes and crimes against humanity."
Although an area in the Vanni region is a government-designated "no-fire" zones for civilians, the Office of the High Commission for Human Rights, based in Geneva, said information indicates shelling continues inside the areas.
Tamil Tigers rebels are believed to be using civilians as human shields and shooting those trying to leave their control, the official said, adding that the human rights agency received reports of the rebels forcibly recruiting civilians as soldiers.
She called on both the government and LTTE to halt fighting immediately to allow civilians to evacuate the war zone, and urged Sri Lankan authorities to give the U.N. and other agencies full access to accurately assess conditions.