Missiles believed fired from a U.S. unmanned plane slammed into a house used by militants in northwestern Pakistan on Thursday, killing seven people, a government official and a witness said.

The identities of the victims in the attack in Kurram region were not immediately known.

A senior official in the region said the house targeted was believed to be frequented by Islamist militants. He spoke on condition of anonymity because he was not authorized to release the information.

Villager Ismail Khan said spy planes were seen hovering over the area shortly before the attack, adding that local militants had retrieved seven bodies from the destroyed house.

The United States has launched more than 30 missile strikes on Al Qaeda and Taliban targets close to the Afghan border since last year, killing many militants, including some senior ones, but also civilians.

The missiles are believed fired from drones launched from neighboring Afghanistan, but the United States rarely acknowledges firing them.

Pakistan routinely protests the attacks as violations of its sovereignty, but many people speculate the two countries have an unwritten deal allowing them.