South Sudan border town Bentiu bombed
Several bombs have been dropped on the South Sudanese border town of Bentiu, amid fears of all-out war with Sudan.
International journalists saw at least two planes drop bombs and a huge plume of smoke rising from a market, where they saw the body of a young boy.
A top South Sudanese military official described the bombing as a "serious escalation" and a "provocation".
It follows weeks of clashes along the border between South Sudan and its northern neighbour.
There was no immediate comment from Sudan's military, but it has always denied carrying out aerial bombardments on South Sudan in the past.
On Sunday, both countries confirmed there was ground fighting in the disputed border region.Troops massing
Those clashes took place south of Heglig, the oil field which has been at the centre of the recent crisis.
Nearly two weeks ago South Sudanese troops seized control, inflicting a serious military and economic blow to Sudan.
On Friday, the South said it was withdrawing its soldiers following intense international pressure, although Sudan said it had forced them out.
Access to the disputed border region around Heglig is limited, making it difficult to verify what is happening in the area.
Main disputes between Sudans
- Transit fees the South should pay Sudan to use its oil pipelines
- Demarcating the border
- Both sides claim Abyei
- The rights of each other's citizens now in a foreign country - there are estimated to be 500,000 southerners in Sudan and 80,000 Sudanese in the South
- Each accuses the other of supporting rebel groups on its territory
The BBC's James Copnall, who is in Bentiu, says it had been hoped that the withdrawal from Heglig would reduce tension but the latest fighting, and aerial bombardments, make it clear this has not happened.
The air raid's main target seems to have been the bridge which provides access to the nearby border region, he says.
The local state governor told the BBC that, as well as the death of the young boy, three people had been critically wounded when a bomb fell on the market.
Witnesses saw several market stalls on fire. The same area was hit just a week ago.
Our correspondent says South Sudan is building up its troops near the border, and is assuming that Sudan is doing the same.
Satellite pictures released over the weekend appear to show that significant parts of the Heglig oil field are no longer operating following the recent fighting.
They were analysed by the US-funded Satellite Sentinel Project (SSP), which says it is impossible to know who was responsible for the damage.
US President Barack Obama and the African Union have called on both sides to resume peace talks.
South Sudan seceded last July as part of a peace deal following two decades of war, which left some 1.5 million people dead.
It took some 75% of the united Sudan's oil with it but all the oil pipelines lead north and the two successor states have not been able to agree on the level of transit fees which the South should pay to use Sudan's pipelines.
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.