A US drone attack has killed at least four militants in a restive northwestern Pakistani tribal area on the Afghan border, officials said Thursday, taking the toll from a flurry of strikes this week to 25.

The drone attack took place at Laman village in North Waziristan where the Pakistani military has been waging a major offensive since June.

"A US drone fired two missiles at a vehicle and killed at least four militants and one was wounded," a senior security official told AFP.

The official said that the drone strike took place before midnight and added that there were "foreigners" among those killed.

A local government official confirmed the casualties.

There has been a spike in drone attacks in North Waziristan this month. Analysts say it could be linked to intelligence regarding a high-value target though none of the casualties so far have been named.

The semi-autonomous tribal region has 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 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 anti-militant offensive in North Waziristan in June and say they have killed more than 1,000 so far, with 86 soldiers losing their lives in the operation.

The area is off-limits to journalists, making it impossible to verify the number and identify the dead independently.

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.