Air strike is first since Pakistan reopened Nato supply route to Afghanistan and comes just before crucial diplomatic meeting
People in Multan, Pakistan, protest against US drone attacks on Saturday.
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.
The apology paved the way for Pakistan to permit trucks carrying Nato supplies to cross into Afghanistan for the first time in more than seven months.
But America appears set to continue with its controversial programme of increased drone strikes.
Last Sunday, eight people were killed in an attack on a suspected militant safehouse. It followed a number of other such strikes in June.
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.
But the use of drones is highly controversial, with a large chunk of the Pakistani public - as well as human rights activists around the world - resenting their use due to the high number of non-military casualties.
Figures from the London-based Bureau of Investigative Journalism show that CIA drones stuck Pakistan 75 times in 2011, causing up to 655 fatalities.
The majority of those killed were alleged militants, but as many as 126 civilians also have lost their lives, the bureau's figures suggest.
Islamabad has demanded for a halt in the US programme of drone attacks and their continued use has strained relations between the two countries.