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

The missiles struck militant compounds in the villages of Haider Khel and Hasookhel 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 missiles on two militant compounds. At least eight militants have been killed," a security official in Miranshah told AFP.

The two attacks occurred within an hour, with four militants killed in each compound, the official said, speaking on condition of anonymity.

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.

US drone strikes last week killed a prominent warlord, who had sent insurgents to fight NATO troops in neighbouring Afghanistan, along with nine other militants in Pakistan's tribal belt.

Mullah Nazir, one of the highest-profile drone victims in recent years, was the main militant commander in South Waziristan, part of the tribal zone where militants linked to the Taliban and Al-Qaeda have bases on the Afghan border.

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.