Foreign fighters, including Uzbeks and Arabs, are believed to be present in the area that was targeted. At least 23 militants have died in the drone attacks carried out in the past six days.
Four militants were killed in a drone strike on May 26 while four more were killed in an attack near Miranshah on May 23. Ten militants, mostly foreigners, were killed in yet another missile strike on May 24.
The US has stepped up drone strikes after the conclusion of the North Atlantic Treaty Organisation Summit in Chicago last week, where Pakistan did not make any announcement about ending a nearly six-month blockade of supply routes to Afghanistan.
The supply lines were shut after a cross-border NATO air strike killed 24 Pakistani soldiers in November last year. The string of drone strikes have added to tensions between the US and Pakistan, which has described the attacks as a violation of its sovereignty and called for them to be stopped.
The US eased its drone campaign in Pakistan's tribal area after a CIA contractor was arrested for shooting and killing two Pakistani men in Lahore early last year.
Washington has been pressing Islamabad to launch a military operation in North Waziristan Agency, which American officials have said is a safe haven for the Haqqani network that has been blamed for a series of brazen attacks on Western targets in Afghanistan.
Pakistan has been resisting US pressure to launch a sweeping offensive against militants in the area, saying its troops have been stretched by operations in other parts of the tribal belt.
US-Pakistan relations have been in free fall since last year, and Islamabad has been insisting that Washington should apologise for the NATO air strike.
US President Barack Obama snubbed Pakistan at the NATO summit by refusing to hold a one-to-one meeting with President Asif Ali Zardari.
Kill Zone: 468 Pakistani lives lost to US drones in 7 months
US drones regularly target terrorists in Pakistan: Obama
Military insect drones are here!
World's best unmanned predators
PICS: This drone can stay in the air for 4 days!