Air strike is first since Pakistan reopened Nato supply route to Afghanistan and comes just before crucial diplomatic meeting.
The death toll from a US drone strike in Pakistan rose to 19 on Saturday, increasing tensions ahead of a meeting between secretary of state Hillary Clinton and her Islamabad counterpart.
Pakistani authorities increased the estimate from an initially reported 12 suspected militants who were killed in the attack in the Dattakhel region in North Waziristan on Friday.
On Sunday, Clinton is due to meet with Pakistan’s foreign minister, Hina Rabbani Khar, in Tokyo. That meeting, on the sidelines of a major conference on Afghanistan, will be given added pique as a result of the increased use of drones by the CIA in recent months.
Friday’s strike came just days after Washington and Islamabad resolved a protracted dispute over the use of unmanned armed aircraft, with Clinton apologising for an air attack that killed 24 Pakistani soldiers in November.
Under a strategic review conducted earlier this year, the Pentagon announced it will increase the number of unmanned armed crafts in its arsenal by almost a third.
Figures from the London-based Bureau of Investigative Journalism show that CIA drones stuck Pakistan 75 times in 2011, causing up to 655 fatalities.