Mediators urged the government and rebels to sign a cease-fire on Wednesday as talks got under way to end a monthlong revolt, but there was little sign either side was ready to make a deal. The rebels have come within striking distance of the capital, Bangui, posing the biggest threat to President François Bozizé since he took control of the mineral-rich country in a rebellion a decade ago. The rebels demand that Mr. Bozizé step down, accusing him of failing to honor a 2007 peace agreement to give insurgents money and jobs. The rebels captured a string of towns, pushing government forces to within 45 miles of Bangui, before bowing to pressure from troops from neighboring nations.