Relations sour as Nato helicopter and Pakistan troops exchange shots

The Nato firing incident took place in the Datta Khel area of the North Waziristan tribal region, a known sanctuary for Taliban and al-Qaida militants who launch attacks inside Afghanistan as well as Pakistan. It has been targeted repeatedly by covert US drone strikes.

A Western military official in Afghanistan and a Nato spokesman said there was firing at the border, but they did not confirm that Pakistani border troops were the target or had been hit.

The Pakistani army, facing internal criticism for failing to detect or stop the unilateral American raid that killed bin Laden, said it lodged a strong protest and demanded a meeting with Nato officials to discuss the incident. Nato said it would investigate.

A similar event last year in which two Pakistani soldiers were killed prompted the army to immediately close a key border crossing to Nato supplies heading from Pakistan into landlocked Afghanistan, dramatically exposing the vulnerability of the war effort.

The Western military official said a Nato base in Afghanistan took intermittent direct and indirect fire from the Pakistani side of the border. Two helicopters flew into the area, and one fired across the border after twice taking fire from the Pakistani side, said the official.

Nato declined to say which coalition country was involved, but most of the helicopters that fly in that part of Afghanistan are American.

Relations between the United States and Pakistan have been tense since the Navy SEALs raid on May 2.

The Pakistani government is outraged that the US carried out the operation without telling Pakistan first, and many US officials have expressed disbelief that bin Laden could have lived in Abbottabad for at least five years without the authorities' knowledge.

Nato said it was still trying to determine whether the helicopter crossed in to Pakistani airspace.

"We're investigating the incident to determine a flight path by examining GPS waypoints in the helicopter computer, to construct a sequence of events and ultimately determine what led to the exchange of fire," said a spokesman.

The Pakistani army said its troops fired on the helicopter after it entered Pakistani airspace in the early hours of the morning. Two of its troops were injured when the helicopter returned fire, it said.

Also today Pakistani security forces shot and killed four would-be suicide bombers, including three women, when they tried to attack an army checkpoint in the south-western city of Quetta.

Security forces stopped the five as they approached the checkpoint in a car, said Junejo. One of the men got out of the car and blew himself up. The other four, who were also wearing suicide vests, were shot when they tried to lob grenades, he said.