A US drone strike on Wednesday killed at least 13 people in a suspected militant compound in Pakistan's northwestern tribal belt, as the country's military wages a major offensive against insurgent hideouts.
The attack came in North Waziristan, where for the past month the Pakistani military has been fighting to wipe out longstanding bases of Taliban and other militants.
Elsewhere in North Waziristan, air strikes in the Shawal Valley killed 35 militants, according to a statement from the military.
"A US drone fired two missiles targeting a militant compound in Zoi Saidgai area, killing at least 13 insurgents," a senior security official in Miranshah, the main town of North Waziristan, told AFP.
The official said there had been reports of militants moving to Zoi Saidgai from Miranshah and Mir Ali, the other main town in the area, after the start of the army operation.
Another security official said as many as 20 people may have been killed in the strike, 12 of them Uzbeks.
He said the attack took place around 2:00 am (2100 GMT Tuesday) while an important meeting was going on in the compound.
Pakistan's semi-autonomous tribal areas on the Afghan border have for years been a hideout for Islamist militants of all stripes -- including Al-Qaeda and the homegrown Tehreek-e-Taliban Pakistan as well as foreign fighters such as Uzbeks and Uighurs.
Washington pressed Islamabad for years to take action to wipe out sanctuaries in North Waziristan, which militants have used to launch attacks on NATO forces in neighbouring Afghanistan.
Jets and artillery began hitting rebel targets on June 15 to try to regain full control of the district and ground forces moved in on June 30.
The assault was launched after a dramatic attack on Karachi airport which killed dozens of people and marked the end of a faltering peace process with the Pakistani Taliban.
More than 400 militants and 25 soldiers have been killed in the assault so far, according to the military, though the area is off-limits to journalists, making it impossible to verify the number and identity the dead independently.
Pakistan routinely protests against US drone strikes, which have been targeting militants in the tribal areas since 2004, saying they are a violation of sovereignty and counterproductive in the fight against terror.
Military officials have also strongly denied suggestions that there has been collusion with the US on drone strikes, which restarted shortly before the North Waziristan offensive after a six-month hiatus.
More than 800,000 people have been forced to flee from North Waziristan by the assault, with most ending up in the nearby town of Bannu.
There have been fears that many top militants also fled, including fighters from the feared Haqqani network which is blamed for numerous bloody attacks in Afghanistan.