US warns of new Sudan-South Sudan conflict over border
Sudan's refusal to accept a border deal with South Sudan could spark an "outright conflict", the US has warned.
The comments were made by the US ambassador to the UN, Susan Rice, following a Security Council meeting on the issue.
South Sudan has accepted the border roadmap proposed by the African Union, but Sudan is refusing to do so.
The two countries came close to an all-out war this year over the disputed border and oil revenues.
South Sudan won independence from Sudan last year, ending decades of fighting between the mainly Muslim north and Christian and animist south.
Speaking in New York, Ms Rice said Khartoum's refusal to sign to the roadmap plan "risks the resumption of outright conflict".
She stressed that it also "calls into question Khartoum's seriousness" to resolve the issue.
Despite South Sudan's acceptance of the plan, Ms Rice said that Washington was "deeply concerned by the apparent lack of urgency" shown by both sides.
The original 2 August deadline set by the UN failed to produce an agreement.
However, both sides are being kept under pressure to clinch a deal by a new deadline - 22 September.
Khartoum and Juba last month held three weeks of talks in the Ethiopian capital Addis Ababa.
They resulted in a provisional oil payments deal, which is subject to further talks on security.
The talks resumed earlier this week. A summit between the presidents should follow to make the deal official.
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.