A US drone fired two missiles at a compound in Pakistan's northwestern tribal district early Thursday, killing at least three militants, local security officials said.

The missiles hit a house in Mubarak Shahi village, in Mir Ali, 20 kilometres (12 miles) east of Miranshah, the main town in the North Waziristan tribal district, which is a stronghold of Taliban and Al-Qaeda-linked militants.

"Militants were using this house as a compound. At least three militants were killed in this drone strike," a security official based in the northwestern city of Peshawar told AFP.

Another security official in Miranshah confirmed the attack and said four militants were killed.

The covert US attacks are unpopular in Pakistan, where the government criticises them as a violation of sovereignty but American officials believe they are a vital weapon against Islamist militants.