Pro-government tribesmen killed 23 militants in clashes in Pakistan's northwest in the latest violence between tribal militias and Taliban insurgents, a government official said Tuesday. Elsewhere in the volatile northwest, suspected militants attacked an oil tanker carrying fuel to NATO forces in Afghanistan, killing two people, an official was quoted as saying by The Associated Press. The clashes between militants and tribesmen took place in the village of Ambar in the Mohmand region. Syed Ahmad Jan, a senior regional administrator, said local tribal militia asked the militants to leave the area late Monday. The militants refused and opened fire, sparking a gun battle that was still raging Tuesday morning, Jan said. Pakistan's government has encouraged tribesmen in the semiautonomous frontier region to form local militias _ known as lashkars _ to repel Taliban militants blamed for attacks in Pakistan and Afghanistan. Such groups have been set up in several regions but face stiff Taliban resistance. The attack on the oil tanker took place in the nearby Khyber region, said Fazal Mahmood, a local government official. The attackers opened fire on the truck, then fled when the security forces escorting the convoy returned fire, Mahmood said. The truck driver and a passer-by were killed. The tanker was not damaged.