Sudan People's Liberation Army spokesman Philip Aguer Monday said rebels attacked a group of soldiers in Upper Nile state Sunday, prompting an SPLA counter-attack. He says seven soldiers and at least 47 militiamen were killed in the fighting.
Aguer said the militia is linked to a former Sudanese foreign minister, Lam Akol, and is being supported by the government of northern Sudan.
Southern officials have accused the north of arming regional militias with the goal of destabilizing south Sudan as it prepares for independence. The south voted overwhelmingly to separate from the south in a January referendum.
Reuters news agency quotes an official with the north's ruling party, Rabie Abdelati, as saying the north wants the south to be strong and stable.
The southern army has also battled a separate militia led by a renegade army officer, George Athor. Hundreds of people have died in those clashes.
Northern and southern Sudan fought a 21-year civil war that ended with a 2005 peace agreement.
Some information for this report was provided by AP, AFP and Reuters.