New satellite images appear to show thousands of Sudanese government troops marching toward a rebel stronghold in a contested region near South Sudan.

The Satellite Sentinel Project released the images Friday, saying at least 3,000 troops appear to be marching on Kurmuk in Blue Nile State. The U.S.-based monitoring group says the forces include heavy armor, artillery, tanks and helicopter gunships.

The Satellite Sentinel Project also said it identified what it claims are craters consistent with artillery or rocket attacks in Dindiro, not far from where the troops have gathered.

Fighting along the border with South Sudan has been escalating since June, about a month before South Sudan split from the north and declared independence.

Clashes earlier this week left dozens dead in the war-torn state of Southern Kordofan.

The opposition rebel group Sudan People's Liberation Movement-North said Wednesday it carried out an attack on government troops killing at least 30 Sudanese soldiers. But a government official rejected reports that the rebels had taken control of parts of the area, telling the semi-official Sudanese Media Center that government troops fought off the attack, killing 30 members of the SPLA and capturing two others.

Khartoum has repeatedly claimed that the South Sudanese military is supporting the rebels in the oil-rich border state, but Juba denies the charges.

Meanwhile, the World Food Program is calling on Sudanese officials to grant the agency full access to both Blue Nile state and South Kordofan.

A WFP spokeswoman told the French news agency both areas are suffering from a lack of food, and that at least 235,000 people are in need of assistance.

Sudan ordered the WFP and other human rights groups to leave the border areas in June, when the fighting began to escalate.