New fighting has broken out in South Sudan, threatening a cease-fire the government and rebels agreed to last month.
South Sudan's army says rebels attacked government positions Tuesday morning in Malakal, the capital of oil-producing Upper Nile state.
A spokesman for rebel forces, Lul Ruai Koang, tells VOA the rebels were responding to government attacks.
The rebels say they have taken full control of the town, which they captured once before. An army spokesman says the rebels seized only partial control.
In a Twitter message, Toby Lanzer, the top U.N. humanitarian official in South Sudan, urged all those involved to respect people's rights and protect civilians.
The warring sides signed a cessation-of-hostilities deal in Ethiopia last month, but both sides have accused the other of breaking the pact.
Two months of violence have left thousands dead and forced more than 850,000 people from their homes.