An intensive bombing campaign in Sudan is causing “huge suffering” for civilians, the UN says.
A UN spokesman said two planes had dropped 11 bombs near the South Kordofan town of Kauda on Tuesday.
Aid workers say pro-southern groups are being ethnically cleansed in the area, while a deal has been done to withdraw troops from the nearby Abyei region.
The fighting comes less than a month before South Sudan is to secede from Africa’s biggest country.
It raises 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 recent clashes.
Although South Kordofan is north of what will soon be the international border, it is home to many pro-south communities, some of whom fought with southern rebels during the long civil war.
“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 by northern forces and that people had fled further into the area’s hills and mountains to escape the attacks.
Aid workers say that some 40,000 people have been forced from their homes in South Kordofan, on top of some 100,000 in Abyei.
Amnesty International’s Tawanda Hondora told the BBC’s Network Africa programme that some people had been arrested outside the UN base in the South Kordofan capital, Kadugli, and were later shot dead.
“We think this is the start of what might be ethnic cleansing of South Kordofan, Unity State and Abyei, with the precise purpose of ensuring that, come independence, the areas will not have people who are perceived to be sympathetic to the south,” he said.
Aid agency offices have been looted, churches have been ransacked and buildings destroyed.
But this was denied by Rabbie Abdelattif Ebaid, an adviser to Sudan’s information minister.
“The armed forces are targeting the rebels. The area has now been freed from all rebels. Everything is now quiet in the main towns,” he said.
On Friday, the south accused the northern military of bombing areas in Unity State to seize oil fields from the south.
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.
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.