A US drone strike in north-west Pakistan has killed two top commanders of one of Pakistan's most influential Taliban groups, officials say.
They say that among the four people killed is the brother of top Taliban leader Maulvi Nazir.
Maulvi Nazir's Taliban faction is based in Pakistan's South Waziristan tribal region where the drone attack on Thursday took place.
His forces are blamed for attacks on Nato troops in nearby Afghanistan.
The militants were killed when four missiles were fired at a pick-up truck they were driving in Azam Warsak, 20km (13 miles) west of Wana, the main town in South Waziristan.
Correspondents say that the strike is a sign that US intelligence has penetrated the close family circle of Maulvi Nazir.
Officials say that local Taliban militants immediately cordoned off the area and closed the road in the aftermath of the attack.
The BBC's M Ilyas Khan in Islamabad says that the Wana region is controlled by militants loyal to Maulvi Nazir.
Officials say one of his top commanders, Khan Mohammad, was also killed in Thursday's strike, as was his brother, Hazrat Omar.
Our correspondent says that Maulvi Nazir is considered close to the Pakistani military and has a peace agreement with them.
Although drone strikes in South Waziristan are not unusual, our correspondent says, this is the most deadly attack yet against the Maulvi Nazir group.
Residents and security officials in the region say that 27-year-old Hazrat Omar was the operational head for the Nazir group and a close ally of his brother.
They said that despite his low profile, he played a key role in assigning duties to fighters in Afghanistan in addition to supervising logistical arrangements for their missions.
Earlier this month a top Haqqani militant commander was killed in a suspected US drone strike in North Waziristan.
Janbaz Zadran was believed to have "played a central role in helping the Haqqani network attack US and coalition targets" in Afghanistan.
Drone attacks frequently target Pakistan's restive tribal areas, where many insurgents have taken shelter.
The frequency of the attacks has increased since President Barack Obama took office in 2008.
More than 100 raids were reported in the area last year and more than 60 have taken place this year.
A number of militants, some of them senior, have been killed in the raids, but many civilians have also died.
The US does not routinely confirm drone operations, but analysts say only American forces have the capacity to deploy such aircraft in the region.
Relations between the US and Pakistan have been severely strained this year and worsened after the killing of al-Qaeda chief Osama Bin Laden on Pakistani soil by US commandos in May.
US Secretary of State Hillary Clinton said on a visit to Pakistan last week that her country would take action within "days and weeks" on dismantling Afghan militant havens in Pakistan in addition to encouraging the Taliban into peace talks.