The strike took place in Landidog village, 20 kilometres (12 miles) west of Wana, the main town in South Waziristan tribal region.

A security official confirmed the attack and casualties but said the "identities of those killed in the strike were not yet known".

The United States does not confirm drone attacks, but its military and its Central Intelligence Agency (CIA) operating in Afghanistan are the only forces that deploy them in the region.

The US strikes are deeply unpopular among the Pakistani public, who see foreign military action on Pakistani soil as a violation of national sovereignty.

Missile attacks doubled in the tribal areas last year as the covert campaign was stepped up, with more than 100 drone strikes killing over 670 people in 2010 compared with 45 strikes that killed 420 in 2009.