A US missile strike on a militant compound in Pakistan's tribal district on the Afghan border killed six rebels on Wednesday, local security officials said.
The strike took place in Dandey Darpakhel village, five kilometres (three miles) northwest of Miranshah, the main town in North Waziristan tribal district, which is a renowned hub for Taliban and Al-Qaeda linked militants.
"Six militants were killed in the US drone strike on a rebels' compound," a senior security official in the area told AFP, adding that the death toll may rise.
It was the fifth missile strike in the region over the past six days.
The official said the nationalities of the militants killed was not yet known.
Another security official in the region confirmed the strike and casualties.
US forces have been waging a drone war against Taliban and Al-Qaeda-linked commanders in Pakistan's northwestern tribal belt, where militants have carved out havens in mountains outside direct government control.
The US military does not as a rule confirm drone attacks, but its armed forces and the Central Intelligence Agency operating in Afghanistan are the only forces that deploy pilotless drones in the region.
More than 1,040 people have been killed in 122 drone strikes in Pakistan since August 2008, including a number of senior militants. However, the attacks fuel anti-American sentiment in the conservative Muslim country.
Washington has branded the rugged tribal area on the Afghan border -- part of which has been hit by Pakistan's catastrophic flooding -- a global headquarters of Al-Qaeda and the most dangerous place on Earth.
Officials in Washington say the strikes are a vital tool needed to protect the 150,000 foreign troops in Afghanistan, and have killed a number of high-value targets including Pakistani Taliban chief Baitullah Mehsud.
Under US pressure to crack down on Islamist havens along the Afghan border, Pakistan has in the past year significantly increased operations against militants in the area.