The United Nations says an upsurge in violence in Sudan's western Darfur region is threatening security and humanitarian aid to hundreds of thousands of people.

U.N. spokeswoman Radhia Achouri says about two-thirds of south Darfur are considered hazardous and no-go areas because of recent attacks on peacekeepers.

In the western Darfur city of Geneina, U.N. staff face increased constraints in delivering aid due to banditry and clashes between rebels and government-backed militias.

In recent days, African Union peacekeepers and civilians have been killed or kidnapped in violence that AU officials have blamed on Darfur's main rebel group, the Sudan Liberation Movement.

More than two million people have been displaced and tens of thousands of others killed during more than two years of conflict.

Some information in this story provided by AP.