Militants ambushed an Afghan military patrol in a Taliban stronghold Tuesday, sparking a three-hour gunbattle that left four troops and two rebels dead, an Afghan official said. The incident was just the latest in a string of attacks and killings blighting the runup to the country's historic presidential election on Oct. 9. The ambush was laid by about 20 gunmen who opened fire on 30 militia soldiers riding pickup trucks through Nawbahar, a mountainous district of Zabul province, deputy police chief Jailani Khan said. "It was a Taliban ambush," Khan said. "They fought it out for three hours with AK-47s and machine-guns until the enemy retreated into the hills." Two militants were killed and two more captured, he said. Four of the Afghan militia soldiers died.