NATO said its aircraft entered Pakistani airspace early Thursday in self defence and killed “several armed individuals” after the crews believed they had been fired at from the ground.

After striking what was believed to be an insurgent group, “the aircraft received what the crews assessed as effective small arms fire from individuals just across the border in Pakistan,” NATO’s International Security Assistance Force (ISAF) said in a statement.

“Operating in self defence, the ISAF aircraft entered into Pakistani airspace killing several armed individuals,” it said.