The US stressed here Thursday that the crisis in South Sudan must be ended "swiftly", calling on rebel leader Riek Machar and President Salva Kiir to "immediately" sign cessation of hostilities agreement. National Security Advisor Susan Rice said in a statement that the US "strongly supports the efforts of the Intergovernmental Authority on Development (IGAD) mediators, Ambassador Seyoum Mesfin and General Lazaro Sumbeiywo, to secure a cessation of hostilities and to resolve the conflict in South Sudan peacefully through talks being held in Addis Ababa, Ethiopia." "This crisis must be ended swiftly through a negotiated settlement in order to prevent the escalation of a dangerous conflict that neither the people of South Sudan, the region or the international community can afford," she stressed. She added that the US calls upon rebel-leader Riek Machar and President Salva Kiir "to sign immediately the cessation of hostilities agreement tabled by IGAD." She noted that Machar, "in particular, must commit to a cessation of hostilities without precondition," stressing that "his continued insistence on the release of detainees as a pre-condition for a cessation of hostilities is unacceptable." Meanwhile, Rice affirmed that the US "is disappointed that the detainees being held by the Government of South Sudan have not yet been released." "The United States reiterates its call upon President Salva Kiir to release the detainees immediately to the custody of IGAD so that they can participate in the political negotiations," she stressed. "It is the obligation of both President Kiir and Mr. Machar to ensure that the lives of their people and future of their young country are not further marred by continued violence and atrocities," she remarked.