South Sudan faces possible famine if warring government and rebel forces do not heed a ceasefire deal they have signed, United States and European Union envoys warned Thursday. "The parties have failed to respect their commitment to the January 23 cessation of hostilities," said US envoy Donald Booth at a meeting of regional leaders in Ethiopia on the conflict in the world's youngest country. "This failure has led to thousands of additional deaths and an ever worsening humanitarian situation, with South Sudan facing a possible famine."