In a sign a new peace deal may not hold, South Sudan's government said Saturday that rebel fighters had attacked government troops after the cease-fire had come into force.

If the attacks continue, government troops will defend themselves, said Information Minister Michel Makeur Lueth. The peace deal was signed Thursday night but did not go into effect for 24 hours, said Lueth.

The minister would not say where the fighting was taking place on Saturday but fighting took place on Friday in Jonglei state. Government leaders had expressed fear that 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 Dec. 15.

Meanwhile, a U.S. based conflict prevention group, the Satellite Sentinel Project, said new satellite images from over South Sudan show that fighting has resulted in the intentional burning of some 750 homes near the town of Bentiu, the capital of oil-producing Unity state.

"This new satellite imagery is visual proof that recent violence and combat on the ground has direct impact on civilians living in Unity State. These scorched earth tactics have destroyed homes and residential areas, and put women, children, and families in great danger," said Akshaya Kumar, the South Sudan analyst for the U.S. based group the Enough Project.

The UN says that gross violations of human rights have taken place during the conflict, which has often pitted the military against ethnic Nuer fighters loyal to Machar.