The officials said missiles from the drones hit two vehicles in the Datta Khel area of North Waziristan, one of seven districts in Pakistan's mostly ungoverned tribal region along the Afghanistan border, a longtime militant stronghold.

The drone strike was at least the second in the past 24 hours and the 49th strike this year.

The officials asked not to be named because they are not authorized to speak to the media on the record.

Another suspected U.S. drone strike killed two militants in Pakistan's tribal region on August 3, intelligence officials have said.