Warring South Sudanese Close to Signing Cease-Fire Leaders for warring sides in South Sudan said Saturday they are close to signing a cease-fire in a monthlong conflict that the UN says has created a "horrifying human rights disaster." Military spokesman Philip Agur, meanwhile, said army forces retook the key city of Bor on Saturday, defeating a coalition of some 15,000 rebels. There are doubts about how much control rebel leader and former Vice President Riek Machar has over some of the forces fighting for him, raising concerns about his ability to reign in all the rebels even if he signs an agreement. In Juba, the capital of South Sudan, presidential spokesman Ateny Wek Ateny said he believed a cease-fire would be signed Sunday or Monday. In Ethiopia, where talks are taking place, rebel negotiator Mabior de Garang said he hoped the agreement would be signed Saturday night. The rebels apparently have made a major concession, according to negotiators, agreeing the cease-fire deal will not be tied to previous demands for the immediate release of 11 key political detainees. That sticking point and other issues, including the withdrawal of Ugandan troops fighting for the government, are to be discussed after a cease-fire is signed and hostilities end, they indicated. De Garang is the son of former rebel leader John Garang, who prosecuted the nearly 40-year rebellion against Sudan only to die months after negotiating a 2005 peace agreement that paved the way for South Sudan's separation from the mainly Arab-led north. The latest conflict threatened to splinter Africa's newest nation along tribal lines and came just 17 months after South Sudan became independent. Fighting broke out Dec. 15 and spread throughout the country after whole army units defected. President Salva Kiir said it began with a coup attempt, a charge the rebels deny. Thousands are believed dead and hundreds of thousands have been forced from their homes. The top U.N. human rights official, Ivan Simonovic, on Friday charged both sides have committed mass atrocities, with mass killings, gruesome atrocities, sexual violence and using children to fight. He called it a "horrifying human rights disaster." The United Nations also has accused both sides of looting from humanitarian organizations. USAID administrator Rajiv Shah on Saturday called for perpetrators to be prosecuted and "immediate and unconditional access" for UN and humanitarian organizations to all areas of South Sudan along with steps to ensure they can operate safely. The United States is the biggest aid donor, with Shah noting it has pledged $320 million to South Sudan for the coming financial year. "Attacks on aid groups must stop and leaders of both parties to the conflict must put an end to the looting of humanitarian supplies," Shah said. Those who have fired on and attacked UN peacekeeping bases, raided UN and NGO offices and warehouses, and killed drivers delivering assistance, must be held to account. Agur, the military spokesman, on Saturday denied troops were involved in stealing and human rights violations, even as he urged soldiers to behave lawfully. Associated Press writers Elias Meseret in Addis Ababa, Ethiopia, and Michelle Faul in Johannesburg contributed to this report.