Pakistani troops backed by helicopter gunships attacked Islamist militants close to the Afghan border, killing 15 of them, a government official said Monday.

The violence Sunday took place in Mohmand tribal region hours after suspected Taliban fighters killed 13 paramilitary police officers.

In late February, the military took journalists to Mohmand and neighboring Bajur and claimed major security gains in both regions.

Meraj Khan, a government representative in Mohmand, said the attack on the militants took place late Sunday in the Salam Koroona area. He had no more details, and the Taliban were not immediately available for comment.

Mohmand and surrounding districts in northwest Pakistan are Taliban and Al Qaeda strongholds.

The militants are believed to use the northwest to attack U.S. and NATO forces in Afghanistan.

Washington is calling on Pakistan to do more to fight the insurgency there and since last year has stepped up attacks by unmanned spy planes.

Over the weekend, there were reports one of the planes either crashed or was shot down over South Waziristan, but the military said it had yet to find any wreckage.