At least four soldiers were killed and 25 wounded when a suicide bomber rammed his explosive-laden car into a military checkpoint in Pakistan's troubled northwest on Wednesday, security officials said. The attack came in the Mir Ali area of Miranshah, the main town in the North Waziristan tribal region, a hub for Taliban and Al-Qaeda linked militants on the Afghan border. "Four security officials embraced shahadat (martyrdom) and 25 were wounded when a suicide bomber hit his explosive-laden car into the mosque of Khajori checkpoint, some three kilometres east of Miranshah," a security official told AFP. "The soldiers were offering prayers at the time of the blast," the official said. No group immediately claimed responsibility for the attack. The umbrella Tehreek-e-Taliban Pakistan faction and Al-Qaeda linked militants have led a bloody campaign against the Pakistani state in recent years, carrying out hundreds of attacks on security forces and government targets, concentrated largely in the northwest.