A US drone strike targeting a vehicle in Pakistan's northwestern tribal belt on Monday killed at least four militants, local security officials said.

The unmanned aircraft fired two missiles, hitting a vehicle and a guest house of a local tribal elder in the Nurak area of North Waziristan, the Pakistani officials told AFP.

The area is within the notorious tribal badlands that Washington calls a global headquarters of Al-Qaeda, .

"The unmanned aircraft fired two missiles at the vehicle and killed at least four militants in the strike," one security official told AFP on the condition of anonymity as he is not authorised to speak to media.

"A guest house of a local tribal elder was also destroyed in the attack. However, it was not immediately known if there was anybody inside the guest house at the time of the attack," he added.

Nurak area is 20 kilometers (12 miles) east of Miranshah, the main town of the district of North Waziristan, considered a militant stronghold.

The security official said initial reports suggested that a group of militants were travelling in the vehicle at the time of the attack.

Two other Pakistani intelligence officials confirmed the drone strike and death toll.

Washington has called Pakistan's semi-autonomous northwest tribal region the global headquarters of Al-Qaeda, where Taliban and other Al-Qaeda-linked networks have rear bases from which they launch attacks on NATO forces in Afghanistan.

Although the United States does not publicly confirm drone attacks, its military and the CIA in Afghanistan are the only forces that deploy the unmanned Predator aircraft in the region.

North Waziristan is the headquarters of the Haqqani leadership and the main militant bastion in the semi-autonomous tribal belt.

The Haqqani network is considered the deadliest enemy of US troops in eastern Afghanistan. It was founded by Jalaluddin Haqqani and is run by his son, Sirajuddin, both designated "global terrorists" by Washington.

The group has been blamed for some of the worst anti-US attacks in Afghanistan, including a suicide attack at a US base in the eastern province of Khost in 2009 that killed seven CIA operatives.

Around two dozen drone strikes have been reported in Pakistan since elite US forces killed Al-Qaeda chief Osama bin Laden in a suburban home near Pakistan's main military academy in Abbottabad, close to the capital, on May 2.

The raid humiliated Pakistan and prompted allegations of incompetence and complicity in sheltering bin Laden.

Pakistan is seen as a key ally for the United States in its fight against Islamist militancy, but relations have soured since the bin Laden raid, which both countries say was carried out without Islamabad being warned.

Drone attacks are unpopular among many Pakistanis, who oppose the alliance with Washington and who are sensitive to perceived violations of sovereignty.

US officials have accused Pakistani intelligence of playing a double game with extremists, including the Afghan Taliban and the Haqqani network, in order to exert influence in Afghanistan and offset the might of arch-rival India.

Washington's pressure on Islamabad to launch a decisive military campaign in North Waziristan, as Pakistan has conducted elsewhere in the tribal belt, has so far fallen on deaf ears.