A Taliban ambush touched off fierce fighting in southern Afghan mountains that left eight police and four rebels dead, officials said Saturday. Insurgents hiding behind rocks attacked the police as they were driving slowly on rough roads in Helmand province late Friday in search of a rebel hideout, said provincial administrator Ghulam Muhiddin. A two-hour gunbattle ensued before the rebels fled, he said.The government sent 200 police reinforcements into the area to hunt down the attackers. The assault was the latest blow for the police force after a string of deadly ambushes in recent weeks. The violence highlights the challenge facing President Hamid Karzai's U.S.-backed government, as well as the 30,000 foreign troops based here, in trying to end a stubborn insurgency that has left more than 1,400 people dead this year. This month has seen a spike in attacks against prominent senior officials, teachers and religious leaders — many of whom had recently spoken out against the insurgents.