The United Nations says 300,000 people in South Sudan have lost access to "life-saving aid" after fighting forced relief groups to withdraw from the town of Leer.
The pullout follows a surge in clashes involving rebel groups and government forces in South Sudan's Unity state. The U.N. warned Friday that the violence has forced up to 100,000 people to flee their homes.
On Monday, the U.N. said all non-governmental organizations and U.N. agencies have evacuated their staff from Leer and some other locations in the state.
Those aid groups include the International Committee of the Red Cross and Doctors Without Borders, which announced Saturday it was suspending operations at its hospital in Leer. That facility was previously burned and looted in January 2014.
The U.N. humanitarian coordinator for South Sudan, Toby Lanzer, warned in a statement that the violence comes at a time when food stocks are depleted, and at the height of the planting season.
He called for the warring sides to allow aid groups to resume their work without delay.
South Sudan has been mired in conflict between soldiers backing President Salva Kiir and rebels who support former vice president Riek Machar for more than a year.
The war has displaced more than 1 million South Sudanese, leaving many dependent on foreign food aid. Peace talks in Addis Ababa, Ethiopia, have made little progress.