"These tensions threaten not only to undermine the political stability and economic progress that both sides have so painstakingly achieved, but also international support for their efforts," Francois Lonseny Fall, the secretary-general's special representative for Somalia, said in a statement released in Nairobi Friday.

Fall asked Puntland, an autonomous section of northeastern Somalia, to cease all hostility with neighboring Somaliland, which declared independence from Somalia in 1991.

Fighting in the southern section of the country between the Ethiopian-backed Transitional Federal Government forces and insurgents has left hundreds dead and wounded. "All the hospitals in the city and its environs have been overwhelmed with the rising number of casualties," Fall said. In addition, tens of thousands of civilians have fled the capital Mogadishu as a result of the conflict.

Fighting in Somalia is heaviest since the outbreak of war a decade ago. Officials including James Swan, U.S. deputy assistant secretary for African affairs, have voiced concern the conflict could destabilize the Horn of Africa.

The U.N. refugee agency began delivering 28 tons of relief supplies to help the nearly 20,000 people who fled recent fighting in Mogadishu Thursday, UNHCR spokesman Ron Redmond said in Geneva.

"Thousands of displaced Somalis have spent nearly two weeks without proper food, water or shelter," Redmond said. "Insecurity in parts of Mogadishu has continued to jeopardize humanitarian access to the Somali capital and surrounding regions, making the plight of civilians all the more desperate."