A US drone strike killed at least seven militants in Pakistan's restive tribal belt on Thursday, including an important commander of the feared Haqqani network, security officials said.

The attack happened early Thursday in Nargas village of Birmil area, some 30 kilometres west of Wana, the main town of South Waziristan tribal region near the Afghan border which is considered a stronghold of Taliban militants.

Officials and a militant source said four foreigners and an important commander from the ruthless Haqqani network, which is blamed for numerous bloody attacks in Afghanistan, were among those killed.

"At least seven militants were killed in the drone strike," an intelligence official based in Wana told AFP, adding that the dead included four foreigners and a top Haqqani commander.

"Abdullah Haqqani (the commander) was responsible for sending suicide bombers to Afghanistan," the official said.

Another official in the neighbouring garrison town of Bannu confirmed the death toll and killing of the commander.

A source in a militant group said that a vehicle loaded with arms and ammunition was also destroyed in the attack.

Pakistan's foreign ministry condemned the drone strike.

"Pakistan has consistently maintained that such strikes are a violation of its sovereignty and territorial integrity," foreign office spokeswoman Tasnim Aslam told reporters in Islamabad.

"Drone strikes and their impact is a subject that is part of our talking points in our engagements with the US from the head of government level to the working level.

"Naturally, the United States has its own position which is not backed by international law and now the international public opinion," she 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 1,100 militants so far, with 100 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 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 at the start of the year -- 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.