The United Nations says 150 people were killed in southern Sudan last week during fighting between government forces and former rebels.
U.N. official, Peter Maxwell says more than 400 other people were wounded in the clashes in the town of Malakal.
The U.N. mission says corpses have contaminated parts of the Nile River, a main source of drinking water in the town.
The fighting in Malakal was between government forces and the Sudan People's Liberation Army. Each side blamed the other for starting the violence.
The United Nations reported Thursday that a tense calm had been restored after three days of fighting.
The violence appeared to be the worst in the region since a peace agreement was signed in January 2005 to end Sudan's 21-year north-south civil war.
U.N. Secretary-General Kofi Annan said the fighting was a serious violation of the peace agreement.
The agreement gave southern Sudan an autonomous government and the right to vote on possible secession from the north in a future referendum.
Some information for this report was provided by AP and Reuters.