According to security sources, the US drone targeted a house in Azam Warsak area, 20 kilometers off Wana, killing at least four people.
Local people said US drones were hovering in the area for hours, stirring panic in among the denizens and signaling air offensive.
AFP adds: The attack happened early Thursday in Nargas village of Azam Warsak district, 25 kilometres (15 miles) west of Wana, the main town of South Waziristan tribal region which is considered a stronghold of Taliban militants.
“Up to four missiles were filed targeting a militant compound, killing four rebels,” a senior security official told AFP on condition of anonymity because he was not authorised to speak to media.
Another security official confirmed the attack and casualties and said that all the militants killed in the strike were foreigners.
“We are currently ascertaining their nationalities,” he added.
South Waziristan is one of the seven lawless tribal districts of Pakistan that border Afghanistan.
These semi-autonomous areas have for years been a hideout for Islamist militants of all stripes — including Al-Qaeda and the homegrown Tehreek-e-Taliban Pakistan (TTP) as well as foreign fighters such as Uzbeks and Uighurs.
Washington pressed Islamabad for years to wipe out the sanctuaries in the North Waziristan tribal area, which militants have used to launch attacks on NATO forces in Afghanistan.
The Pakistani military launched a major offensive in North Waziristan in June and say they have killed more than 1,000 militants so far, with 86 soldiers losing their lives in the operation.
The area is off-limits to journalists, making it impossible to independently verify the number and identity of the dead.
The army assault, codenamed “Zarb-e-Azb” after a sword used in battle by the Prophet Mohammad, was launched after a dramatic attack by militants on Karachi airport, which killed dozens of people and marked the end of faltering peace talks between the government and the Pakistani Taliban.
Pakistan routinely protests against US drone strikes, which have been targeting militants in the tribal areas since 2004, saying they violate its sovereignty and are counterproductive in the fight against terror.
But most analysts believe the resumption of the drone programme after it was suspended — reportedly to give Pakistan space for negotiations with the Taliban — is evidence of collusion between the two countries.
The Islamabad government and military officials strongly deny this.