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The attack took place in Wacha Bibi, 50 kilometres (30 miles) west of Miranshah, on Tuesday morning with two NATO helicopters entering Pakistani airspace from Afghanistan and attacking the checkpoint, they said.
"Two NATO helicopters committed the airspace violation and shelled an army checkpoint, injuring two soldiers," a senior security official told AFP.
The incident came after the United States launched a raid from Afghanistan on May 2 that killed Al-Qaeda leader Osama bin Laden near Islamabad.