Gunmen shot dead a mid-level Pakistani Taliban commander in the lawless northwestern tribal belt on the Afghan border on Monday, security officials said. Pakistani officials said they were not aware of the motive for the killing but intelligence officers said it could be a result of internal differences within the Islamic militant group. Shakirullah Shakir, 45, was riding a motorcycle in the Kutab Khel area, just east of Miranshah, the main town of North Waziristan tribal district, when he was mowed down. \"Gunmen sprayed bullets at his passing motorcycle and Shakirullah was killed on the spot,\" a security official in Miranshah told AFP, requesting anonymity. Washington calls Pakistan\'s semi-autonomous tribal belt the global headquarters of Al-Qaeda, whose leader Osama bin Laden was killed by US forces in Pakistan on May 2. Government officials said they were not aware of a bounty out for Shakirullah, described as a mid-level commander, but said he was believed to be important because of his affiliation with a wing of Taliban suicide bombers called Fidayeen-e-Islam. The killing came following the defection earlier Monday of a Pakistani Taliban warlord who claims to control hundreds of foot soldiers. Fazal Saeed told AFP by telephone that he had broken with the militia and would form his own anti-American group along the Afghan border. Saeed described himself as the leader of Pakistan\'s umbrella Tehreek-e-Taliban (TTP) faction in the tribal district of Kurram, but said he had run out of patience with the network for killing civilians. TTP has claimed a series of high-profile attacks in the nearly two months since US troops killed bin Laden in a night-time raid. The covert American raid has brought Pakistani-US ties to their lowest point since Islamabad abandoned support for the Taliban regime in neighbouring Afghanistan and joined the US-led war on terror.