A US drone is suspected of firing four missiles at a vehicle in north-western Pakistan, killing six alleged militants, intelligence officials said.
The officials said the attack took place in the Datta Khel area of North Waziristan, part of Pakistan's lawless tribal region near the Afghan border.
The identities and nationalities of the suspected militants killed were not immediately known.
The area where the attack took place is dominated by fighters loyal to prominent militant commander Hafiz Gul Bahadur.
The US has dramatically stepped up such attacks in the past year in an attempt to kill Taliban militants who use Pakistani territory to launch attacks against foreign troops in Afghanistan.
Many of the strikes have taken place in North Waziristan, part of Pakistan's semi-autonomous tribal area which is almost entirely dominated by a variety of militant groups. The US has pushed Pakistan to launch a military offensive in the area, but the government has resisted.
The US wants Pakistan to target Bahadur - a prominent commander focused on battling foreign troops in Afghanistan - and other militants in North Waziristan, but many analysts think the government is reluctant to go after fighters who have not set their sights on attacking the Pakistani state.
Some of the militant groups also have historical ties to Pakistani security forces and could be useful allies in Afghanistan after foreign forces withdraw.
Given Pakistan's reluctance, President Barack Obama's administration has stepped up its reliance on drone strikes.
The US refuses to discuss the attacks in public, but many officials have said privately that they have killed senior Taliban and al Qaida militants.