The top UN humanitarian official in South Sudan, Eugene Owusu, said in a statement that both government and opposition forces in the Upper Nile region beat aid workers in separate incidents.
"Humanitarians are in this country to save lives. It is beyond reckoning that they continue to be killed, harassed and abused despite our repeated calls for action," Owusu said.
He also called an attack by government forces on the southern town of Pajok that killed several dozen people "reprehensible". The attack sent thousands of people fleeing into neighbouring Uganda, worsening what has become the world's fastest-growing refugee crisis.
South Sudan officials also continue to restrict aid workers. An order from the Northern Leich state government, dated today and obtained by The Associated Press, requires all aid organisations to seek the authorities' approval to hire new staff. It also requires the groups to hand over all assets once projects end.
The Bentiu UN displacement camp in Northern Leich is the largest in South Sudan, sheltering 1,17,000 civilians who fled the fighting.
Tens of thousands of people have been killed since the civil war began in December 2013. Famine was declared in two counties in Unity state in February, with hundreds of thousands of people threatened.