Obama says ceasefire 'critical first step' to South Sudan peace

WASHINGTON (Reuters) - President Barack Obama said on Thursday he welcomed the ceasefire between South Sudan's government and rebels, but added that leaders need to work to resolve the underlying causes of the conflict, and must quickly release political detainees. "South Sudan's leaders must demonstrate their sustained commitment to a peaceful resolution of the crisis," Obama said in a statement. "They have an obligation to ensure that the lives of their people and future of their young country are not further marred by continued violence, and that individuals who have committed atrocities are held to account." (Reporting by Roberta Rampton. Editing by Andre Grenon)