Sudan and South Sudan are both claiming to be in control of the Heglig oil fields, despite assurances from the Southern government that it is withdrawing its troops to avert a return to war.
The countries have given different accounts of the withdrawal. Early Friday, South Sudan said it was commencing an orderly and voluntary pullout from Heglig immediately.
Later that evening, however, South Sudan's ambassador to the United Nations, Agnes Oswaha, told reporters at U.N. headquarters in New York that southern forces were still in complete control of Heglig. She did confirm that all southern forces would be out of Heglig within 72 hours.
"The Republic of South Sudan took this decision because it does not wish to see a return to war and seeks an immediate resumption of negotiations between the two parties," said Oswaha.
Meanwhile, Sudan's ambassador to the United Nations, Daffa-Alla Elhag Ali Osman, said earlier that Sudanese forces had retaken Heglig by force.
"It's a pleasure and great honor for me and with great jubilation I convey to you that our heroic Sudanese Armed Forces have chased out the aggressors from Heglig," said Osman.
Ali Osman said Sudan is ready to resume talks with South Sudan if, in his words, the south's leaders "come to their senses" and negotiate without conditions.
Noting the withdrawal, United Nations Secretary-General Ban Ki-moon issued a statement calling on the governments of both countries to resume negotiations "immediately."
In Washington, U.S. State Department spokeswoman Victoria Nuland said the United States is urging South Sudan to fully withdraw all forces from Heglig, and is calling on Sudan to immediately end any reprisal attacks.
"In parallel, we are also calling on the government of Sudan as we have regularly to halt their own cross-border attacks, particularly the provocative Arial bombardments, so that we can get back to a place where these two sides are working together and using mechanisms like the joint-border verification and monitoring mechanism to work through their issues," said Nuland.
South Sudan seized the Heglig oil fields on April 10, sparking fears of all-out war between the two countries. In a speech Wednesday, Sudanese President Omar al-Bashir threatened to crush South Sudan's government like an "insect."
The South's information minister said Friday that Juba still considers Heglig to be part of its territory and wants the status of that area and other contested regions to be determined by international arbitration.
The two Sudans have been unable to resolve disputes over borders, oil, and citizenship stemming from the South's independence last July.
Chief disputes include the future of the oil-producing Abyei region and the sharing of oil revenue. The South took over three-fourths of Sudan's oil fields when it separated, but uses northern pipelines for export.
The countries have been fighting along their disputed border but the U.S. special envoy to Sudan, Princeton Lyman, said Thursday that both sides want to avoid a larger conflict.
"In the discussions I have had in both Khartoum and Juba, I can say with confidence that virtually everyone I have talked to has said, 'Look we don't want to go to all-out war with the other. We need to find a way out," said Lyman.
Before their separation, north and south Sudan fought a 21-year civil war that eventually led to southern autonomy and independence.