The United States has intensified missile strikes by drone aircraft in Pakistan's lawless Pashtun tribal lands in an effort to curb violence in Afghanistan, much of which U.S. officials say comes from militant sanctuaries on the Pakistani side.

Most of the missile attacks this year were carried out on militant targets in the North Waziristan region.

In the latest strike, the missiles hit a house used by militants as a hideout near Mir Ali, the second major town of the region.

"We have reports that 12 militants were killed in the attack. The death toll could be more," an intelligence official in the region told Reuters.

He said Amir Moawia, an important Pakistani Taliban commander, was among the dead.

Another intelligence official said there were five foreigners among the slain militants but their nationalities could not be immediately confirmed.

A large number of militants linked to al Qaeda and the Taliban, including Arabs, Uzbeks, Chechens and Chinese fled to Pakistani border regions and took refuge with their Pakistani allies after the U.S. invasion of Afghanistan following the al Qaeda attacks on the United States in 2001.

Pakistan is a key U.S. ally in its efforts to stabilize Afghanistan but it officially objects to U.S. missile strikes and says they infringe on its sovereignty though analysts believe that the strikes are carried out with the tacit approval of Pakistan.

Pakistani forces are themselves fighting homegrown militants and have killed hundreds of militants and destroyed many bases in their strongholds in the northwest over the past year. The militants have unleashed a campaign of reprisal bomb and suicide attacks across the country, killing hundreds of people in recent months.