Humanitarian agencies working in Darfur told U.N. officials the Sudanese government launched an aerial attack on a primary school last weekend, killing at least 13 people.

Officials with the United Nations and the African Union said the opposition Sudan Liberation Army controls the region and has seen "repeated aerial attacks and possible fighting between government and rebel forces during the course of the last few days," the U.N. integrated regional information networks said.

U.N. and A.U. officials said the escalating conflict threatens to derail ongoing peace negotiations. Disputes over the Darfur Peace Agreement fractured three main rebel movements into 28 different factions, all of them suspicious of the peace process.