A US drone strike killed four suspected militants in North Waziristan on Friday, the third such attack in 48 hours, officials said. The drone fired two missiles into a vehicle as it drove through Darpa Khel village about four kilometres (two miles) west of Miran Shah, the main town in the district of North Waziristan, the Pakistani security officials told AFP. The US drone fired two missiles, one of the officials told AFP on condition of anonymity because he was not authorised to talk to the media. Four militants were killed in the attack, they were all in the vehicle, he added. Since 2008, the United States has regularly unleashed unmanned drone-fired missiles against militants in the border region. Pakistani officials protest the strikes, which are unpopular among many Pakistanis, but the country is believed to support them privately and makes no diplomatic or military efforts to stop them.