The presidents of Sudan and South Sudan "must have the courage" to return to the negotiating table and resolve their differences peacefully, says US President Barack Obama.He was speaking after South Sudan said it had ordered its troops to withdraw from the Heglig oil field in Sudan.Within hours of Friday's announcement, Sudan said it had retaken Heglig town.South Sudanese forces captured the area last week, accusing Khartoum of using it as a base to launch attacks."We know what needs to happen," said President Obama. "The government of Sudan must stop its military actions including aerial bombardments."It must give aid workers the access they need to save lives. And it must end its support for armed groups inside the South."Turning to the government of the newly independent South Sudan, Mr Obama said: "Likewise, the government of South Sudan must end its support for armed groups inside Sudan and it must cease its military actions across the border.The escalating fighting and rhetoric between the two sides over the past week has led to fears of all-out war.It is not clear whether Khartoum regained the area by force or whether South Sudanese troops withdrew, under intense international pressure.South Sudan said its forces were still in the process of withdrawal; Information Minister Barnaba Marial Benjamin told AFP it would take three days to complete the operations.President Omar al-Bashir on Friday told supporters at a victory rally in Khartoum: "We thank God that he made successful your sons; and the security forces and the police force and the defence forces - he has made them victorious on this Friday."South Sudan has so far made no public comments on Khartoum's claim.South Sudan seceded last July following a 2005 peace deal that ended a two-decade civil war in which more than 1.5 million people died.On Thursday, South Sudan issued a statement saying it was not interested in war with its northern neighbour and that it would only withdraw from Heglig if the UN deployed monitors there.President Bashir had earlier threatened to bring down the government in Juba following the loss of Heglig, which provided more than half of Sudan's oil.South Sudan's President Salva Kiir said the South still believed that Heglig was a part of South Sudan and that its final status should be determined by international arbitration, Associated Press reported.Heglig is internationally accepted to be part of Sudanese territory - although the precise border is yet to be demarcated.Other issues dividing the two countries are the transit fees the South should pay Sudan to use its oil pipelines and the status of the province of Abyei.