Juba , South Sudan ( CNN ) -- A growing chorus of international agencies is calling for South Sudan 's warring factions to cease hostilities . A day after East African leaders warned both the fledgling country and its rebel group to lay down their arms within four days , U.N. Secretary-General Ban Ki-moon threw his weight behind that ultimatum from the Intergovernmental Authority on Development ( IGAD ) . In a statement released Saturday , Ban said he lauded IGAD for `` appointing a mediation team to work with the government of south Sudan and opposition in reaching a cease-fire , the release of the detainees and building toward a process of peaceful dialogue . '' `` The United Nations stands with the people of South Sudan and will continue to do everything within its means to protect civilians at risk and provide necessary humanitarian assistance , '' the U.N. statement continued . `` All violence , attacks and human rights abuses must end immediately . The Secretary-General reminds those responsible that they will be held accountable . He calls on the government and all concerned to ensure the rights and security of civilians are protected . '' It 's unclear what the repercussions would be for either side if they refuse the demands . A communique issued Friday in Nairobi , Kenya , appears to throw IGAD 's weight behind South Sudanese President Salva Kiir , whose government has said that it would come to the negotiating table without preconditions . Kiir has accused rival politician Riek Machar , his former vice president , of trying to stage a coup -- a claim Machar has denied . Kiir 's Vice President , James Wani Igga , says Machar will make it difficult for both sides to meet IGAD 's truce deadline . `` Dr. Riek has put obstacles to this genuine call by issuing preconditions : namely that the cease-fire or peace can not be reached unless a negotiation is conducted , and added a number of obstacles , '' the South Sudanese Vice President said Saturday . Kiir and Machar are longtime rivals from two different tribal clans . Kiir is from the Dinka tribe , Machar from the Neur . Fighting broke out between Kiir 's government and supporters of Machar on December 15 in the capital city of Juba . It quickly spread across the country , with reports of mass killings lent credence by mass graves . Worried about the safety of medical staff and facilities , Doctors Without Borders is also asking both sides to alleviate `` the volatile and rapidly evolving security situation . '' The international aid group says it has provided medical care to approximately 40,000 people who have fled to two U.N. bases in Juba since the latest wave of violence began . The U.N. says more than 63,000 total civilians are now crowded onto its compounds across South Sudan . Even though a curfew is in place in Juba , and though the capital has been relatively safe and stable compared to other parts of South Sudan for the past week or so , scared and beleaguered civilians have refused to leave the U.N. compounds . On Friday , 72 peacekeepers arrived in Juba , according to the United Nations . It was the first group of an additional 5,500 peacekeepers approved by U.N. Security Council . The additional personnel will increase the total peacekeeping force in South Sudan to 12,500 soldiers and 1,323 police officers . CNN 's Arwa Damon and journalist Mading Ngor reported from Juba , South Sudan , and CNN 's Mark Morgenstein wrote this story in Atlanta .
U.N. Secretary-General Ban Ki-moon backs East African leaders ' call for peace . Ban warns those responsible for violence and human rights abuse 'will be held accountable ' Doctors Without Borders also calls for end to violence .