Looters in South Sudan have stolen more than 3,700 tonnes of food, enough to feed 220,000 people for a month, the World Food Programme said on Friday.
The U.N. agency's warehouses in Malakal had been almost emptied, spokeswoman Elisabeth Byrs told a UN briefing in Geneva. The agency was working to recover lost stocks wherever possible and trying to protect remaining stocks, she said.
The loss will hamper efforts to feed the 73,000 civilians who have taken refuge in UN bases as well as more than 200,000 refugees who have been relying on UN support in Upper Nile and Unity states since before the latest crisis began.
A total of 494,000 people have been uprooted across South Sudan, the UN says.
South Sudan's government and rebels signed a ceasefire on Thursday to end more than five weeks of violence that divided Africa's newest nation and brought it to the brink of civil war.
"In this kind of situation it's very difficult to protect food stocks," Byrs said, adding that she had no details on how the looting had happened.
The ceasefire is expected to be implemented within 24 hours of the signing, but there were doubts from diplomats that the depth of the ethnic, political and personal grievances would be easy to overcome.
WFP is seeking $57.8 million for emergency food aid for South Sudan, and expects to need to ask for more in future.
WFP has reported no looting of its food stocks so far in another African crisis, in Central African Republic.