In a sign a new peace deal may not hold, South Sudan's government says rebel fighters have attacked government troops after the ceasefire had come into force.
If the attacks continue, government troops will defend themselves, Information Minister Michel Makeur Lueth said on Saturday.
The peace deal was signed on Thursday night but didn't go into effect for 24 hours, Lueth said.
The minister wouldn't say where the fighting was taking place on Saturday but fighting broke out on Friday in Jonglei state.
Government leaders had expressed fear whether fighters in Jonglei known as the White Army would abide by the deal.
"These are rebels and they are undisciplined people and not a regular force and have no central command, and for that matter it is not strange that they immediately violated it," he said.
The peace deal "was not a waste of time. We will try our level best to ensure our people that the cessation of hostilities is properly effected and monitored", he added.
The conflict between government forces and rebels loyal to former Vice President Riek Machar has forced 500,000 people from their homes and killed thousands since hostilities broke out December 15.
