Sudan's South Kordofan: 'Huge suffering from bombs'
The UN has accused the Sudanese government of carrying out an "intensive bombing campaign" near the north-south border.
This has led to "huge suffering" for civilians in South Kordofan, it says.
Northern forces are accused of targeting the area's pro-southern groups, as oil-rich South Sudan prepares for independence next month.
The bombing follows a deal for both sides to withdraw from the nearby disputed town of Abyei.
Clashes over the past month in Abyei and South Kordofan have raised fears of renewed north-south conflict despite a 2005 peace deal which paved the way for the end of decades of war.
Some 140,000 people have fled the fighting.
Although South Kordofan is north of what will soon be the international border, it is home to many pro-south communities, especially in the Nuba Mountains, some of whom fought with southern rebels during the long civil war.
"We are extremely concerned about the bombing campaign, which is causing huge suffering to the civilian population and endangering humanitarian assistance," Kouider Zerrouk, spokesman for the UN mission in Sudan, told AFP news agency.
He said two of the bombs had landed near the UN base in Kauda, close to an airstrip that was apparently being targeted. Mr Zerrouk said the bombing started a week ago.Aid agencies looted
In addition, aid workers say, ethnic Nubans are being targeted by the northern military and Arab militias.
"People are being hunted down for their ethnicity," John Ashworth, an adviser with the Sudan Ecumenical Forum, told the BBC's Focus on Africa programme.
He said many areas inhabited by ethnic Nubans were being bombed and shelled and that people had fled further into the area's hills and mountains to escape the attacks.
But this was denied by Rabbie Abdelattif Ebaid, an adviser to Sudan's information minister, who said rebel fighters were being targeted.
Some 40,000 people are estimated to have fled their homes in South Kordofan, on top of some 100,000 in Abyei, which was seized by northern forces last month.
Amnesty International's Tawanda Hondora said he suspected a well-planned campaign was being implemented, to rid South Kordofan, Unity State and Abyei of "people who are perceived to be sympathetic to the south."
Aid agency offices have been looted, churches have been ransacked and buildings destroyed.
Talks between Sudanese government officials and representatives of the south are continuing following Monday's deal for both sides to withdraw from Abyei.
President Omar al-Bashir and southern leader Salva Kiir agreed that Abyei, claimed by both sides, would be demilitarised with Ethiopian troops ensuring security.
However, no time frame has been published.
Ahead of the south's independence, the BBC's Peter Martell in South Sudan says several issues have yet to be resolved:
- How to share Sudan's oil wealth - it is currently 50-50
- The demarcation of the border
- Citizenship criteria for the two countries
The north-south war ended with a 2005 peace deal, under which the mainly Christian and animist south held a referendum in January on whether to secede from the largely Arabic-speaking, Muslim north.
Some 99% of voters opted for independence. President Bashir said he would accept the verdict of the south, where most of Sudan's oil fields lie.
Both Sudan and the South are reliant on their oil revenues, which account for 98% of South Sudan's budget. But the two countries cannot agree how to divide the oil wealth of the former united state. Some 75% of the oil lies in the South but all the pipelines run north. It is feared that disputes over oil could lead the two neighbours to return to war.
Although they were united for many years, the two Sudans were always very different. The great divide 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. South Sudan is covered by green swathes of grassland, swamps and tropical forest.
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.
The health inequalities in Sudan are illustrated by infant mortality rates. In South 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 the two Sudans, 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 both countries. In Sudan, many of the residents of war-affected Darfur and the border states of Blue Nile and South Kordofan, depend on food aid. The UN said about 2.8m people in South Sudan would require food aid in 2013. The northern states tend to be wealthier, more urbanised and less reliant on agriculture.