NATO justified the helicopter strikes on Pakistani soil based on “the right of self-defence”, said a spokesman. U.S. officials have said they have an agreement that allows aircraft to cross a few kilometres into Pakistani airspace if they are in hot pursuit of a target.

The first strike took place on Saturday after insurgents based in Pakistan attacked an outpost in Afghanistan's eastern province of Khost, which is located right across the border from Pakistan's North Waziristan tribal area, said U.S. Capt. Ryan Donald, a spokesman for the NATO-led International Security Assistance Force in Afghanistan.

“The ISAF helicopters did cross into Pakistan territory to engage the insurgents,” said Captain Donald. “ISAF maintains the right to self-defence, and that's why they crossed the Pakistan border.” The strike killed 49 militants.

The second attack occurred when helicopters returning to the border were attacked. It killed at least four militants.

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