NAIROBI, Kenya (AP) — A South Sudanese government offensive in the Jonglei region has displaced roughly 100,000 civilians, the United Nations said Thursday, causing aid workers to relocate from an area that has dire humanitarian problems.

A report from the U.N's office of humanitarian affairs said that fighting in the Waat and Walgak areas last week caused scores of thousands of civilians to flee, as well as 60 aid workers.

The U.N. warned the government offensive may exacerbate food insecurity in the Jonglei region, which has some areas that are on the brink of famine. Food drops in one area of Jonglei have been suspended as a result of the fighting, the U.N. said.

"The guns have to fall silent ... (or) the humanitarian situation will continue to deteriorate," said Eugene Owusu, the top U.N. humanitarian official in South Sudan at a press conference on Wednesday in the capital of Juba.

Famine was declared in two countries of South Sudan this February, but aid workers have repeatedly been blocked from delivering food aid by government and rebel forces.

In Jonglei, aid organizations are also fighting what the U.N. calls the longest running outbreak of cholera since South Sudan became an independent nation in July 2011. South Sudan's Ministry of Health has recorded 5,995 cases of cholera, and 146 deaths due to the disease.

The cholera outbreak will "intensify and spread during the upcoming rainy season due to continued conflict," the U.N. humanitarian report on Thursday said.

Roughly 3.5 million people have been displaced due to South Sudan's civil war, according to the U.N, and close to 1 million people have fled to Uganda. Roughly 1 million people in South Sudan are on the brink of starvation, said the report.