NATO says fired on from Pakistani checkpoint

KABUL (Reuters) - The NATO-led International Security Assistance Force (ISAF) in Afghanistan said its helicopters were fired on from a Pakistani military checkpoint along the eastern border on Thursday.

There were no reports of any damage to the helicopters or any casualties, it said.

Frustrated by an intensifying Taliban insurgency in Afghanistan, the United States has stepped up attacks on militants in Pakistan with six missile attacks and a helicopter-borne ground assault this month.

Pakistan strongly condemned the raids and said it would not tolerate any infringement on its territory. The Pakistani army has vowed to stand up to aggression across the border.

"The incident took place at 1330 local Afghan time (0900 GMT). There were two OH-58s and they were 11.5 km (7 miles) on the Afghan side of the border in Tanai district of Khost Province and they were conducting a routine operation," a U.S. military spokeswoman said.

"They received small arms fire from a Pakistani military checkpoint. The helicopters didn't cross into Pakistani airspace," she said.

Neither the helicopters, light attack and reconnaissance aircraft, nor ground forces returned fire, the spokeswoman said.

The unit tried seven times to contact the Pakistani military to find out what was going on, but was unable to make contact, she said.

Most ISAF troops in eastern Afghanistan are American.

ISAF said it was working together with the Pakistani military to resolve the latest incident. A Pakistani military spokesman said he had no information as yet about any such incident.

(Writing by Jonathon Burch; Editing by Jerry Norton)