A US drone strike on Monday killed three militants in Pakistan's northwestern tribal region, a hotbed of Taliban insurgents near the Afghan border, officials said.

The drone fired two missiles into a moving vehicle as it drove through a village near Mubarak Shah town about 15 kilometres (nine miles) east of Miranshah, the main town in North Waziristan district, Pakistani security officials told AFP.

"Three militants have been killed in the attack," one security official said.

"The vehicle was moving. There are reports that four militants were killed in the strike but we are verifying the death of the fourth militant. We have confirmed the death of three others."

The identities of the dead were not clear.

A similar attack on Sunday killed four militants in Datta Khel town about 30 kilometres (20 miles) west of Miranshah.

Covert CIA drones are the chief US weapon against Taliban and Al-Qaeda militants who use Pakistan's lawless tribal areas as launch pads for attacking US troops in Afghanistan and plotting attacks on the West.

Under President Barack Obama, the United States has drastically stepped up drone strikes in Pakistan but it refuses to discuss them publicly.

The latest attack is the 60th US drone strike reported in Pakistan so far this year.

Dozens of them have been launched since Navy SEALs killed Al-Qaeda leader Osama bin Laden in the garrison city of Abbottabad, close to the capital Islamabad, on May 2.

Relations between Pakistan and the United States deteriorated after that, and again over accusations that Pakistani intelligence was involved with the Haqqani network, blamed for a siege in September of the US embassy in Kabul.

Around 2,000 Pakistanis staged a demonstration outside the national parliament in Islamabad Friday to demand an end to US drone strikes, claiming they kill more innocent civilians than extremist leaders.