A US drone fired missiles into a vehicle, killing four militantsMonday in Pakistan's Taliban and Al-Qaeda hub of North Waziristan that hugs the Afghan border, security officials said.
It was only the third such US attack reported in the nuclear-armed state so far this year, following a moratorium after US firepower inadvertently killed 24 Pakistani soldiers in November, plunging relations to an all-time low.
The attack took place at Degan village, some 25 kilometres (15 miles) west of Miranshah, the main town of North Waziristan, the Pakistani officials said.
"A US drone fired two missiles into a vehicle and four militants were killed," a senior security official told AFP on condition of anonymity because he was not authorised to speak to the media.
Local intelligence officials said the dead militants were from Turkmenistan, but their exact identities were not immediately known.
"The vehicle burst into flames after the missiles hit. Militants have cordoned the area and (are) taking out the bodies," a local official told AFP.
US officials say Pakistan's tribal belt provides sanctuary to Taliban fighting for 10 years in Afghanistan, Al-Qaeda groups plotting attacks on the West, Pakistani Taliban who routinely bomb Pakistan and other foreign fighters.
North Waziristan is the most notorious of all Pakistan's seven semi-autonomous tribal districts and has been a major focus of US pressure on the Islamabad government to take sterner action against Afghan insurgents.
Sixty-four US missile strikes were reported in Pakistan's semi-autonomous tribal belt last year, down from 101 reported in 2010 according to AFP tallies.
The United States refuses to discuss drone strikes publicly, but the programme has dramatically increased as the Obama administration looks to withdraw all foreign combat troops from Afghanistan by the end of 2014.
The Pakistani government was understood to assent to the programme despite popular opposition at home and drones have reportedly killed dozens of Al-Qaeda and Taliban operatives and hundreds of low-ranking fighters since 2004.
But the missile strikes fuel widespread anti-American resentment, especially high since the deadly US air strikes on November 26.
A US-NATO investigation blamed the deaths on a catalogue of errors and botched communications on both sides. But Pakistan rejected the findings, insisting the strikes had been deliberate.
Islamabad is now reviewing its entire alliance with the United States and has kept its Afghan borderclosed to NATO supply convoys for two months.
It ordered US personnel to leave Shamsi air base in western Pakistan, widely believed to have been a hub for the CIA drone programme, and is thought likely to only reopen the Afghan border by exacting taxes on convoys.