The World Food Program has condemned the killing of two of its delivery truck drivers in Darfur, Sudan, warning that such attacks are hampering aid operations.

The United Nations food agency says the drivers were shot by gunmen Sunday in two separate incidents on the road between Ed-Daen and Nyala in South Darfur.

An assistant to one of the drivers was wounded. Three other WFP trucks were targeted that same day but no one was hurt.

The WFP said the attacks are making it very difficult to deliver enough food before the rainy season when roads become impassable.

Agency officials are meeting with Sudan's government to discuss the situation.

The United Nations estimates more than two million people displaced by the Darfur conflict need humanitarian aid.