At least four militants were killed and four others wounded Tuesday when a US drone fired missiles at a militant compound in a lawless Pakistani tribal area, security officials said.

The missiles struck a militant compound in Haider Khel village, some 25 kilometres (15 miles) east of Miranshah, the main town in the North Waziristan tribal district, a stronghold of Taliban and Al-Qaeda-linked militants.

"US drones fired four missiles at a militant compound. At least four militants have been killed," a security official in Miranshah told AFP.

Another security official in the northwestern city of Peshawar confirmed the attack and casualties. Both officials said the identity of those killed was not yet known.

The covert US drone strikes are publicly criticised by the Pakistani government as a violation of sovereignty but American officials believe they are a vital weapon in the war against Islamist militants.

Legal lobby group Reprieve estimates that up to nearly 900 civilians were among the 2,621 to 3,442 people killed by drones in Pakistan since 2004.