'Militant base'

Earlier, two people were killed in a missile strike on two houses close to the main district town of Miranshah.

"The American drone fired two missiles, killing two militants and badly damaging a house and an attached guest portion. A car was completely destroyed," the AFP news agency quoted a security official based in Miranshah as saying.

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"The militants rented out this house and were using it as a base."

Unmanned drones are often the weapon of choice for the United States as it targets the Taliban and al-Qaeda in remote, rugged areas along Pakistan's border with Afghanistan. But the US military has rarely confirmed the attacks.

The use of so-called Unmanned Aerial Vehicles (UAVs), which allow the military to operate in highly dangerous areas, is expected to grow in the coming years with the US defence department expected to buy 700 next year alone.

But the long-distance, remote-controlled warfare has sparked public anger for inflicting heavy civilian casualties.

The US government has called on Islamabad to step up its efforts against Taliban- and al-Qaeda-linked fighters who cross over into Afghanistan.

The Pakistani army recently completed an offensive against the Taliban in South Waziristan, which borders North Waziristan.

But Pakistani authorities say the military may soon pursue similar operations in other parts of the lawless tribal belt along the Afghan border.