A US drone strike destroyed a vehicle in Pakistan's tribal belt on Tuesday, killing four militants in the second drone attack since the killing of Osama bin Laden, local officials said.
A security official said the drones fired two missiles into South Waziristan, one of seven districts in Pakistan's semi-autonomous tribal belt on the Afghan border that Washington has called an Al-Qaeda headquarters.
Another official said the missiles fell near Angoor Adda village.
"Two missiles were fired on a vehicle at about 4:15 pm (1115 GMT) and four militants were killed," the official told AFP on condition of anonymity.
The identity of the militants was not immediately known.
On Monday, hundreds of Taliban rallied in the main town of South Waziristan, vowing to avenge bin Laden's death after US Navy SEALs last week shot him dead in the Pakistani town of Abbottabad, near Islamabad.
The last drone strike was on Friday when a salvo of missiles struck a compound in North Waziristan, killing eight suspected militants including Al-Qaeda members, according to officials.
US missile attacks doubled last year, with more than 100 drone strikes killing over 670 people, according to an AFP tally, and the CIA has said the covert programme has severely disrupted Al-Qaeda's leadership.
But some experts say the discovery last week of bin Laden living hundreds of kilometres from the tribal area, in a garrison city not far from the capital, exposes the limits of drone strikes to hit top terror targets.
The strikes inflame anti-US feeling, which has soared this year since a CIA contractor shot dead two Pakistani men in a busy Lahore street in January, and worsened in the wake of the covert US raid on bin Laden's house a week ago.
A drone attack in March saw Pakistan lodge a particularly forceful public protest over the deaths of civilians, although the campaign is believed to operate with the tacit consent of the government in Islamabad.
The surgical operation by US Navy SEALs in the early hours of May 2, seemingly carried out without the knowledge of Islamabad or the country's powerful military leadership, has caused widespread embarrassment in Pakistan.
Prime Minister Yousuf Raza Gilani sought to defend the country in a speech to parliament on Monday, fending off charges of complicity or incompetence over the raid as "absurd" and criticising US "unilateralism" on its soil.
Gilani also insisted Pakistan reserves the right to "retaliate with full force," although he stopped short of spelling what, if anything, would be done if the US staged another high-profile anti-terror raid.