Washington Post Foreign Service

Friday, September 26, 2008; A18

ISLAMABAD, Pakistan, Sept. 25 -- Pakistani troops and a U.S.-Afghan ground patrol exchanged fire Thursday near a frontier checkpoint, U.S. and Pakistani officials said, in a new heightening of armed tension between allies in the war against Taliban insurgents.

According to the U.S. Central Command, the incident began when Pakistani troops at the checkpoint opened fire on two small American helicopters that were providing air support to the U.S.-Afghan unit while it was on patrol near the border. In response, Americans in the patrol fired shots into a hillside on which the checkpoint stood. Pakistani forces then fired on the patrol. The firing ended after about five minutes and the patrol left the area.

U.S. accounts say neither the patrol nor the copters, Kiowa OH-58s, crossed the border. Pakistan disagreed. "When the helicopters passed over our border post and were well within Pakistan territory, our own security forces fired anticipatory warning shots. On this, the helicopters returned fire and flew back," a Pakistani military statement said. It said nothing about a ground patrol.

The United States has been urging Pakistan to move forcefully against Taliban havens in its mountainous border regions, complaining that guerrillas cross into Afghanistan to stage attacks. At the same time, U.S. forces have stepped up their own attacks on suspected hideouts in the restive tribal region of Waziristan, mostly using Predator drones; this month, helicopter-borne commandos went in for a ground strike.

This has led to deep anger in Pakistan's ruling circles. Pakistan's Prime Minister Yousaf Raza Gillani on Wednesday told journalists that Pakistan would not tolerate any act against its sovereignty and integrity in the name of the war against terrorism. Earlier, an army spokesman said any U.S. troops crossing into Pakistan would be fired on.

In many places, confusion is common concerning the precise location of the border and the identities of ground forces. In June, U.S. aircraft attacked armed men who American officials said were shooting at an Afghan patrol from atop a ridge. The Pakistan government said the attack killed 11 of its soldiers.

In recent days, Pakistanis have reported other incidents of Pakistanis firing on American and NATO-alliance helicopters. U.S. officials have denied those reports, saying that no helicopters were in the area at the time.

Rear Adm. Greg Smith, a spokesman for the Central Command, said that the ground patrol in the incident Thursday was close to a mile from the border and that the aircraft stayed out of Pakistani airspace. "Certainly we have to learn what went on in the minds of the Pakistani unit," Smith said, adding that Pakistani officers have said higher approval is needed to engage U.S. forces.

U.S. forces need to be able to communicate with Pakistani forces along the border, Smith said. There was no indication the U.S. troops were able to do that with the Pakistani position, known as Checkpoint 16.

Pakistani checkpoints along the border are manned by Pakistani army soldiers and the locally recruited Frontier Corps. U.S. officials said Frontier Corps members are vulnerable to intimidation by insurgent groups.

Pakistan's chief military spokesman, Maj. Gen. Athar Abbas, said an investigation was underway. He said Pakistani troops had clear orders not to fire across the border.

Tyson reported from Washington.