U.S. military authorities announced today that a brief shootout erupted between U.S. and Pakistani troops along the Afghan border Sunday, prompting the U.S. forces to call in an F-16 warplane that dropped a 500-pound bomb on the Pakistanis to end the clash.

One U.S. soldier was shot and wounded as the encounter began, the U.S. military said in a statement at Bagram, just north of Kabul, the capital. The soldier, whose identity was withheld, was flown to Germany for medical treatment and was listed in stable condition at a military facility there, the statement said.

Reports from Pakistani officials in South Waziristan, the tribal administrative zone on the Pakistani side of the border, said at least two members of the Pakistani Border Scouts were killed in the bombing, which they said hit a Muslim religious school on the Pakistani side of the border in which some of the Border Scouts had taken refuge.

U.S. and Pakistani military authorities sought to play down the clash and stressed that both sides remain determined to cooperate in hunting down remnants of Taliban and al Qaeda forces who have redoubts in the isolated border hills and move back and forth across a tense and loosely policed frontier. But the shooting raised again the question of whether some Pakistani soldiers and tribal leaders still sympathize with their Taliban neighbors, whom they long supported until the Sept. 11, 2001, attacks on the World Trade Center and the Pentagon.

"This was the first incident of its type, but such things happen when a climate of high tension surrounds the borders," said a Pakistani army spokesman. "The matter has since been resolved bilaterally, and a mechanism has been devised to prevent recurrence of such incidents."

The shooting took place near a U.S. base at Shkin, in Afghanistan's Paktika province, 150 miles south of Kabul. A soldier with the U.S. Army's 82nd Airborne Division, Sgt. Steven Checo, 22, of New York, was killed when gunfire broke out in the same area Dec. 21 in what the Army described as an encounter with Taliban or al Qaeda guerrillas.

Those guerrillas were said to have retreated into Pakistan after the clash. The tribal area of South Waziristan is known to be a stronghold of pro-Taliban and pro-al Qaeda families. Despite the presence of 60,000 to 70,000 Pakistani troops along the border, the Pakistani military has been reluctant to carry out intrusive search operations in tribal areas for fear of offending religious sensitivities and disturbing a long tradition of independence for the heavily armed population.

Details of Sunday's shooting and the subsequent bombing remained unclear -- including exactly where it happened. A U.S. military spokesman, Maj. Steve Clutter, said the incident occurred in a "gray area" between Pakistan and Afghanistan along the Durand Line, which was defined in the 19th century by the British and is often disputed or ignored by both sides. A Pentagon official said, however, that the military believes both the shooting and the bombing took place inside Afghanistan.

U.S. military spokesmen here said the wounded U.S. soldier was on a joint mission with a Pakistani Border Scouts unit when one of the Pakistani soldiers opened fire. They said the attacker apparently wore a Border Scouts uniform and had approached a U.S. patrol in a way that concerned the U.S. soldiers.

At the time, the U.S. and Pakistani troops were preparing to blow up some weapons and ammunition they had recently uncovered. Clutter said the Americans warned the approaching Pakistani not to come closer and to return to the Pakistani side of the border. He started to move back but then turned around, crouched down and began shooting with a G-3 automatic rifle, the U.S. spokesmen recounted.

Just before opening fire, Clutter said, the Border Scout spoke to some of his Pakistani colleagues, but it was not known what he said. It was also not known whether he was in fact a Border Scout or was just wearing the uniform.

"The [wounded] soldier was a member of a patrol assisting a Pakistan unit on a routine mission," Clutter said. "A Pakistani Border Scout opened fire with a rifle after the U.S. patrol asked him to return to the Pakistan side of the border.

"That individual and several others retreated to a nearby structure," Clutter said. "Close air support was eventually requested, and one 500-pound bomb was dropped on the target area. We are working with the Pakistanis for an accurate battlefield damage assessment from the incident."

Clutter said it was unknown how many Pakistanis might have been killed. Special Forces and 82nd Airborne soldiers were in the area when the shooting occurred, but military officials would not say which group the wounded soldier belonged to.

Clutter said the incident occurred right on the border, in an area where U.S. troops have been very active lately. He said troops are "operating in those areas with freedom," but that small pockets of "enemy resistance" remain. Those fighters have been regularly launching small rockets at U.S. positions and engaging in brief gun battles when confronted, raising tensions considerably.

"They feel the noose tightening, and they don't like what we're doing," he said.

Special correspondent Kamran Khan in Karachi, Pakistan, contributed to this report.