South Sudan training Darfur rebels - Bashir adviser
An adviser to Sudan's President Omar al-Bashir has accused southern leaders of training rebels from Darfur in order to destabilise the north.
Mustafa Ismail Osman was responding to accusations from the south that the north was stirring up trouble ahead of southern independence in July.
He warned the south that its support for Darfur would not be tolerated.
Tensions are again rising between north and south, after years of war which left some 1.5 million people dead.
The SPLM party, which fought Khartoum for decades until a 2005 ceasefire and now runs the south, has recently accused the north of backing rebel groups in the south and suspended talks about secession.
It has dismissed Mr Osman's allegations.
The western region of Darfur, which will remain part of the north, has faced its own rebellion since 2003.
One of the militia groups fighting the SPLM in South Sudan is led by Gen George Athor who went into rebellion after losing elections last year to be governor of Jonglei state, which he contested as an independent candidate.
Mr Osman told the BBC's Focus on Africa programme that the Khartoum government had nothing to do with supplying Gen Athor with arms, although he said they may have come from the north.
"But we warn the southerners, instead of discussing with us who is supporting Athor… it should be asked: 'What are you doing with Darfur rebels?'" he said.
"We already told them if you're going to destabilise the north, the north doesn't need to come to south in order to destabilise the south.
"We cannot tolerate the south to try to destabilise the north - and we'll just sit down and watch."
Paul Akaro, the SPLM's UK spokesman, said it was "nonsense" to think the southern government would support the Darfur rebels.
He said it was impossible as Juba lacked the resources to support any military activities and it backed the peace process for Darfur.
"When we accused the north, we accused them on the basis of evidence," he told the BBC.
"They are trying to impose instability in the south in order for them to continue pumping oil to the north - that's unacceptable."
Gen Athor's group signed a ceasefire just before January's independence referendum but fighting resumed in February and hundreds have been killed.
President Bashir, who is wanted for war crimes in connection with the conflict in Darfur, has promised to recognise the south's independence.
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.