South Sudan has signed a ceasefire with the largest of several rebel groups which threaten the stability of the world's newest nation, the government said on Tuesday.

The deal to integrate an estimated 1,800 guerrilla fighters into the South's army comes after rebel chief and renegade general George Athor was killed by government forces in December.

South Sudan on Monday accused its former foes in the Khartoum government of arming gunmen who killed over 40 people in a cattle raid, as the U.N. warned tensions between the two sides risk regional peace.

"A militia group from Unity state penetrated into Warrap state... and attacked people in a cattle camp, killing over 40," said Interior Minister Alison Manani Magaya, the latest wave of violence in the world's newest nation.

The Sudanese army claimed a strategic victory on Saturday in its war against the rebels in South Kordofan, saying it captured camps on a key supply route in the southern border region after deadly clashes.

"Today the Sudanese army took control of SPLA camps in the Lake Jau area. The fighting took place at around 4:30 pm (13:30 GMT). There were a number of casualties and injured soldiers on both sides," army spokesman Sawarmi Khaled Saad told Agence France Presse.