A military official had said earlier that armed groups were believed to have been hiding at the house and seven of them were killed and several wounded.

Local officials and the official Associated Press of Pakistan (APP) news agency said there were 16 dead, while state-run Pakistan Television gave a toll of 20 fatalities.

It was not clear who fired the missiles, but villagers said they had heard the sound of a pilot-less drone in the sky before the blasts.

US forces have used drones to fire missiles at armed groups on the Pakistani side of the border several times in recent years.

Major-General Athar Abbas, a Pakistani military spokesman, said there were reports of blasts and some casualties in the area and the military was checking.

Abbas also said Pakistani forces had not carried out any operation in the area and he did not know who carried out the strike or what type of weapon was used.

Neither US nor Pakistani authorities officially confirm US missile attacks on Pakistani territory, which would be an infringement of Pakistani sovereignty.

Pakistan, an important US ally despite widespread public opposition to the US-led campaign against al-Qaeda and the Taliban, says foreign troops would never be allowed to operate on its territory.

Al-Qaeda haven

Many al-Qaeda members, including Uzbeks, Arabs and Taliban took refuge in North and South Waziristan, as well as in other areas on the Pakistani side of the border after US-led forces ousted the Taliban in Afghanistan in 2001.

From sanctuaries in the lawless border belt, the Taliban has orchestrated its offensives against the Afghan government and the US and Nato forces supporting it.

Increasingly, Pakistani members of the Taliban have been mounting attacks in Pakistani towns and cities, many aimed at security forces and other government targets.