NAIROBI, Kenya (AP) — Civilians and aid workers in South Sudan have seen an alarming rise in attacks and harassment in the past week, the United Nations said Saturday, as the East African country faces both civil war and famine.

The top U.N. humanitarian official in South Sudan, Eugene Owusu, said in a statement that both government and opposition forces in 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 neighboring Uganda, worsening what has become the world's fastest-growing refugee crisis.

The U.N. says its peacekeepers repeatedly have been denied access to Pajok by South Sudan's government, a violation of its operating agreement.

South Sudan officials also continue to restrict aid workers. An order from the Northern Leich state government, dated Saturday and obtained by The Associated Press, requires all aid organizations to seek authorities' approval to hire new staff. It also requires the groups to hand over all assets once projects end.

The Bentiu U.N. displacement camp in Northern Leich is the largest in South Sudan, sheltering 117,000 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 in February, with hundreds of thousands of people threatened.