U.S., Pakistani troops exchange fire

By David Morgan

WASHINGTON (Reuters) - U.S. and Pakistani ground forces exchanged fire across the Afghanistan-Pakistan border on Thursday, the latest in a string of incidents that has ratcheted up diplomatic tension between the two allies.

No casualties or injuries were reported after Pakistani forces shot at two U.S. helicopters from a Pakistani border post. U.S. and Pakistani officials clashed over whether the American helicopters had entered Pakistan.

The incident follows a U.S. campaign of attacks on militant targets inside Pakistan, including a Sept. 3 U.S. commando raid on a village compound in South Waziristan. Islamabad has protested those strikes and warned it would defend itself.

"Just as we will not let Pakistan's territory be used by terrorists for attacks against our people and our neighbors, we cannot allow our territory and our sovereignty to be violated by our friends," Pakistani President Asif Ali Zardari said in New York on Thursday.

But in Washington, Pentagon spokesman Bryan Whitman insisted the helicopters had not entered Pakistan. He described the incident as "troubling" and called on Islamabad for an explanation.

"The flight path of the helicopters at no point took them over Pakistan," he said. "The Pakistanis have to provide us with a better understanding of why this took place."

According to Pakistan's military, its soldiers fired warning shots at two U.S. helicopters after they intruded into Pakistani airspace. The U.S. military said the helicopters were protecting a patrol about one mile (1.6 km) inside Afghanistan when Pakistani forces opened fire.