Sudan warned Thursday it could shut its border with South Sudan just weeks after reopening crossings, accusing Juba of backing insurgents battling Khartoum.
South Sudan became independent from Sudan in 2011 under a peace deal that ended a 22-year civil war, but Juba and Khartoum have traded allegations the other is supporting rebels on their territory, which both deny.
"If the government of South Sudan does not stop supporting the insurgents, we might take measures to protect the security of our country and we might even close the border with South Sudan again," Ibrahim Mahmoud, a senior aide to President Omar al-Bashir, told reporters after officials met African Union mediator Thabo Mbeki in Khartoum.
Bashir ordered the reopening of the frontier with South Sudan on January 27 after years of tense relations between the countries, including disputes over several border areas.
Mahmoud said Khartoum could also withdraw the special status accorded to nearly 200,000 South Sudanese who have taken shelter from their country's civil war in Sudan since December 2013.
The South Sudanese are not granted refugee status but are theoretically entitled to the same rights as Sudanese citizens.
Khartoum could scrap this and "treat South Sudanese present in our country according to international law" if Juba does not stop backing rebels battling the Sudanese government in the South Kordofan and Blue Nile regions, Mahmoud said.
The comments came ahead of an AU-mediated meeting in Addis Ababa between Sudanese officials and rebels from South Kordofan, Blue Nile and the western Darfur regions to discuss the conflicts in Sudan's border regions.