By James Copnall BBC News, Khartoum
The African Union says it is deeply concerned about the humanitarian situation in Southern Kordofan.
The state, which borders the south of Sudan, has been the site of fierce clashes in the last two weeks.
South Sudan is due to split from the north next month, but Southern Kordofan is in the north of the country.
The African Union (AU) says hundreds of thousands of civilians have been displaced because of fighting in the state, including aerial bombardment.
The clashes are between rebels from the Nuba mountains, and the north’s armed forces.
Many Nuba fought on the side of the southern army which won independence for South Sudan, and they largely voted against the north’s governing party in recent state elections.
The AU also said allegations of human rights abuses should be investigated.
Khartoum has been accused of “ethnically cleansing” the Nuba, who define themselves as African rather than Arab, making them a minority in northern Sudan.
The AU called for an immediate end to the fighting.
Talks are continuing in the Ethiopian capital, Addis Ababa.
On Monday, northern and southern Sudan agreed to a security solution for the disputed border region of Abyei, which borders South Kordofan.
The northern armed forces took control of the town last month.
They will withdraw, to be replaced by Ethiopian peacekeepers, although a detailed timetable has not yet been set out.
However, there is still no agreement on whether Abyei should be part of Sudan or South Sudan, which will become Africa’s newest nation on 9 July.
Sudan: A country divided
The great divide across Sudan is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. Southern Sudan is covered by green swathes of grassland, swamps and tropical forest.
Sudan’s arid northern regions are home mainly to Arabic-speaking Muslims. But in Southern Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own traditional beliefs and languages.
The health inequalities in Sudan are illustrated by infant mortality rates. In Southern Sudan, one in 10 children die before their first birthday. Whereas in the more developed northern states, such as Gezira and White Nile, half of those children would be expected to survive.
The gulf in water resources between north and south is stark. In Khartoum, River Nile, and Gezira states, two-thirds of people have access to piped drinking water and pit latrines. In the south, boreholes and unprotected wells are the main drinking sources. More than 80% of southerners have no toilet facilities whatsoever.
Throughout Sudan, access to primary school education is strongly linked to household earnings. In the poorest parts of the south, less than 1% of children finish primary school. Whereas in the wealthier north, up to 50% of children complete primary level education.
Conflict and poverty are the main causes of food insecurity in Sudan. The residents of war-affected Darfur and Southern Sudan are still greatly dependent on food aid. Far more than in northern states, which tend to be wealthier, more urbanised and less reliant on agriculture.
Sudan exports billions of dollars of oil per year. Southern states produce more than 80% of it, but receive only 50% of the revenue, exacerbating tensions with the north. The oil-producing region of Abyei was due to hold a separate vote on whether to join the north or the south, but it has been postponed indefinitely.
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Sudan: African fears for Kordofan