Nairobi - South Sudan's government and opposition groups have failed to reach a political agreement mediated by Uganda's president in the latest setback to efforts to end the country's civil war.The text of the agreement obtained by The Associated Press is aimed at unifying the fractured political landscape. But no rebel group that has taken up arms against South Sudan's government signed.An opposition spokesperson, Mabior Garang, dismissed the effort as "political machinations."Uganda has said it is near the breaking point after taking in several hundred thousand fleeing South Sudanese in recent months. It has become the world's fastest-growing refugee crisis.South Sudan President Salva Kiir earlier this week announced another unilateral cease-fire, but reports of fighting have continued. The civil war has killed tens of thousands since December 2013.