Sudan Abyei dispute: Gunmen burning and looting - UN
The Sudanese town of Abyei has been set on fire, with gunmen looting property, the United Nations says.
The town and surrounding area are claimed by both Khartoum and by South Sudan, set to become independent in July. The town was captured at the weekend by northern troops.
The UN has urged Sudan's government in Khartoum to withdraw its forces.
Sudanese President Omar al-Bashir later said that Khartoum wanted to resolve the issue peacefully.
South Sudan's secession follows decades of north-south conflict and some fear this dispute could reignite the war.
'Act of war'
In a statement, the UN Mission in Sudan (Unmis) said it "strongly condemns the burning and looting currently being perpetrated by armed elements in Abyei town".
It stressed that the northern troops were "responsible for maintaining law and order in the areas they control", urging Khartoum to "intervene to stop these criminal acts".
South Sudan earlier denounced the Abyei takeover on Saturday as an act of war.
A southern military spokesman told the BBC the north had attacked the area with 5,000 troops, killing civilians and southern soldiers.
Some 20,000 people, almost the whole population of the town, had fled, aid agency Medecins Sans Frontieres (MSF) told the BBC.
Khartoum has said it acted after 22 of its men were killed in a southern ambush last Thursday. The northern troops were travelling in a UN convoy.
UN officials have described the incident as "a criminal attack" and the US called on South Sudan to "account" for the assault.
South Sudanese forces have denied responsibility for the incident.
Since then, both UN Secretary General Ban Ki-moon and EU top diplomat Catherine Ashton have condemned the violence in the region.
On Sunday, UN Security Council envoys said during a visit to Khartoum that the north should "withdraw immediately" its troops from the Abyei region. The diplomats have now arrived in South Sudan.
Tension over Abyei - a small town claimed by a southern group, the Dinka Ngok, and northern nomads, the Misseriya - has been rising since a referendum on its future scheduled for January was postponed.
Since then there have been fears clashes in the region could spark a new war between the northern-based government of Sudan and the soon-to-be independent South Sudan.
Under a 2005 peace agreement, which ended 22 years of civil war, Abyei was granted special status and a joint north-south administration set up in 2008.
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.