Sudan: Further violence in Abyei border region
There has been further violence in Sudan's disputed Abyei border region, with both southern and northern armies accusing each other of attacks.
The UN confirmed reports of artillery fire in Todac and Tadjalei, just north of the town of Abyei, on Friday.
Earlier, it said a bridge linking Abyei to the south of the country had been nearly hit in an aerial bombardment.
It comes a day after a UN peacekeeping convoy came under attack while escorting northern troops out of Abyei.
The UN described the incident as "a criminal attack", while the US called on South Sudan to "account" for the assault.
"The United States deplores a reported attack yesterday of southern forces on a UN convoy," a state department official said on Friday.
Observers warn the escalating situation in the oil-producing Abyei region risks igniting a new north-south civil war.
South Sudan is due to become independent in July, but disagreement remains over Abyei, which is claimed by both.
On Friday, Abyei's chief administrator, Deng Arop Kuol, told the BBC that artillery fire and possible aerial bombardments could be heard north of the town of Abyei.
The UN said that a bridge linking Abyei to the south had come under attack either from missiles or bombs launched from an aircraft, without giving further details.
It later confirmed "hearing artillery exchanges north of Abyei" in Todac and Tadjalei.
The southern army said northern forces had attacked soldiers and police in at least four villages.
"They used shells, long-range artillery, even tanks," a spokesman told the Reuters news agency.
On Thursday, the northern army claimed it had lost 22 soldiers after an alleged ambush on a convoy by southern troops.
The UN said the northern troops were being escorted out of Abyei by UN peacekeepers.
It not identify the attackers but said the incident took place in an area controlled by southern police forces.
Two northern soldiers and one peacekeeper were injured, the UN said.
South Sudanese forces have denied responsibility for the incident.
A US state department spokesman said the attack was "in direct violation" of the agreement signed by the north and south in January to "remove all unauthorised forces" from Abyei.
"We urge the government of southern Sudan to account for this attack, take steps to demonstrate its commitment to implement the Kadugli agreement, and ensure that its forces demonstrate restraint," he said.
"Political leaders on both sides must take responsibility now to ensure that this situation does does not escalate into a wider crisis."
The violence comes ahead of a planned UN Security Council visit to the area on Monday.
The BBC's James Copnall in Khartoum says the incidents indicate the situation in Abyei has degenerated seriously.
Our correspondent says that although there have been a series of battles around Abyei, direct clashes between northern and southern armed forces have been rare.
Most fighting in the area has been between the Dinka Ngok and the Misseriya, northern nomads who spend part of every year there seeking pastures for their cattle.
Both groups have accused the other side of receiving help from uniformed officials.
In January, the residents of South Sudan voted in a referendum to secede from the north.
A draft version of South Sudan's interim constitution explicitly claims Abyei is in the south.
President Omar al-Bashir has threatened not to recognise the new state if it tries to claim Abyei.
The Abyei region was meant to have its own referendum on whether to join the north or the south in January, but agreement could not be reached on whether the Misseriya could vote.
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.