A satellite monitoring group says Sudan is on the verge of mounting a final assault against the Nuba people seeking refuge against bomb attacks in Southern Kordofan state.

The U.S.-based Satellite Sentinel Project says images show Sudanese government forces have cut off the main evacuation routes in Kauda Valley, where at least 200,000 Nuba people are staying.

Sudan has been battling Nuba rebels accused of supporting South Sudan, which split from the north in July.

Nathaniel Raymond, who helped analyze the images, told VOA the satellite pictures show that new roads and military hardware surround Kauda Valley. He added an airstrip is being lengthened to accommodate warplanes.

In recent months Sudan has carried air and ground attacks in Southern Kordofan, displacing tens of thousands of people and forcing many to flee into neighboring South Sudan.

The United Nations has expressed concern about the situation in the state. Khartoum has denied a U.N. request to allow aid workers to enter the area strictly to provide humanitarian assistance.

A similar situation exists in Sudan's Blue Nile state, where government forces are also battling pro-southern rebels.