At l east four people were killed Friday in a suspected US drone attack on a vehicle in South Waziristan, a security official said. The attack was carried out in South Waziristan, one of seven tribal districts along the Afghan border, where al-Qaeda linked Taliban militants are thought to be active. The vehicle was hit by two missiles, an official said. 'The identity of those killed in the strike is not known,' he said on condition of anonymity. Pakistani authorities have asked Washington to halt the attacks as they kill civilians and anger the local population. But the US says the strikes are necessary to hit militants involved in cross-border attacks on western forces in Afghanistan. It was the first drone attack after Pakistan's political and military leaders met Thursday to discuss deteriorating relations with the US. Friday's U.S. drone strike is the 54th of its kind in Pakistan's northwestern tribal areas in 2011. To date, a total of 470 people, most of them believed to be militants, have reportedly been killed in such strikes.