WASHINGTON (AFP) - President Barack Obama is calling on Sudan's warring factions to end the bloody violence threatening a peace agreement as the south gears up for independence due in three weeks. "There is no military solution," Obama said in an audio message recorded late Tuesday for the publicly-funded VOA broadcasting network. "The leaders of Sudan and South Sudan must live up to their responsibilities. The government of Sudan must prevent a further escalation of this crisis by ceasing its military actions immediately, including aerial bombardments, forced displacements and campaigns of intimidation." His appeal for a ceasefire, taped after returning to the US mainland from a visit to Puerto Rico, came amid a surge of violence that has seen more than 1,500 people killed in south Sudan since a largely peaceful independence referendum in January, according to UN and official figures. Heavy fighting has swept across South Kordofan state on the south Sudan border since June 5 pitting the northern Sudanese Armed Forces and allied militiamen against fighters aligned with southern former rebel group the Sudan People's Liberation Army. Other clashes in south Sudan have killed almost 100 people in separate cattle raids and rebel attacks in the past week, officials said Wednesday.