Two NATO helicopter gunships Thursday fired missiles into a Pakistani border post along the Afghan frontier, killing three soldiers, Pakistani security officials said, DPA reported.
Three more soldiers were injured in the attack at Mandato Khando post in Pakistan's Kurram tribal district, a known hotbed of Taliban and al-Qaeda fighters who cross into Afghanistan for raids on NATO-led international forces.
All those killed and injured were from the paramilitary Frontier Corps, which is deployed to guard the border.
"Our forces have taken up suitable security measures to respond to such acts of aggression, which will be known to the people very soon," a senior Frontier Corps official said.
It was the third alleged violation of Pakistani territory by NATO helicopters in less than a week, but the first attack on the military.
Over the weekend NATO helicopters targeted suspected militants retreating into Pakistan after an attack on international troops in Afghanistan. Dozens of alleged insurgents were killed.
Pakistan strongly condemned the violation of its sovereignty, and warned of an appropriate response.
The latest incident could intensify tensions between the US and Pakistan, allies against the Islamist insurgency in the border areas between Pakistan and Afghanistan.