NAIROBI, Kenya — A U.N. humanitarian report and aid workers caught in the crossfire reported on Wednesday an increase in violence in a new front near the already tense internal border between north and south Sudan, with dozens of people reported killed in attacks.

The violence in South Kordofan has killed at least 25 people, a U.N. humanitarian report said, though it said local sources indicated that up to 64 people had been killed. The north also bombed an airstrip, preventing the movement of food aid and humanitarian workers.

The increased violence comes less than a month before Southern Sudan will declare independence from the north on July 9, the culmination of a 2005 peace deal that ended more than two decades of civil war that killed some 2 million people.

But the sudden outbreak in violence on multiple fronts has greatly increased fears of renewed war, with some aid workers in the south indicating the northern government of Khartoum may be moving toward wider conflict.

Deng Alor Kuol, the minister for regional cooperation for Southern Sudan, said the African Union talks are focusing on empowering an Ethiopian peacekeeping mission for Abyei.

A cease-fire in South Kordofan seems far away. Deng said there are political issues to be addressed first with Abdul Aziz Al Hilu, the leading pro-southern political figure in South Kordofan, before any agreement that would be “effective” and accepted on the ground.