American Maj. Larry J. Bauguess was killed and three other American officers were wounded, along with their Afghan interpreter, in what fresh accounts from the Afghan and American officers who were there reveal was a complex, calculated assault by a nominal ally. The Pakistanis opened fire on the Americans, who returned fire before escaping in a blood-soaked Black Hawk helicopter.

The attack, in  on May 14, 2007, was kept quiet by Washington, which for much of a decade has seemed to play down or ignore signals Pakistan would pursue its own interests, or even sometimes behave as an enemy.

The reconstruction of the attack, which several officials suggested was revenge for Afghan or Pakistani deaths at American hands, takes on new relevance given the worsening rupture in relations between Washington and Islamabad, which has often been restrained by Pakistan’s strategic importance.

The details of the ambush indicate Americans were keenly aware of Pakistan’s sometimes duplicitous role long before Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, told the Senate last week Pakistan’s intelligence service was undermining efforts in Afghanistan and had supported insurgents who attacked the American Embassy in Kabul this month.

Though both sides kept any deeper investigations of the ambush under wraps, even at the time it was seen as a turning point by officials managing day-to-day relations with Pakistan.

Pakistani officials first attributed the attack to militants, then, when pressed to investigate, to a single rogue soldier from the Frontier Corps, the poorly controlled tribal militia that guards the border region. To this day, none of the governments have publicly clarified what happened, hoping to limit damage to relations. Both the American and Pakistani military investigations remain classified.

“The official line covered over the details in the interests of keeping the relationship with Pakistan intact,” said a former United Nations official who served in eastern Afghanistan and was briefed on the events immediately after they occurred.

“At that time in May 2007, you had a lot of analysis pointing to the role of Pakistan in destabilizing that part of Afghanistan, and here you had a case in point, and for whatever reason it was glossed over,” he said. The official did not want to be named for fear of alienating the Pakistanis, with whom he must still work.

Exactly why the Pakistanis might have chosen Teri Mangal to make a stand, and at what level the decision was made, remain unclear. Requests to the Pakistani military for information and interviews for this article were not answered. One Pakistani official who was present at the meeting indicated the issue was too sensitive to be discussed with a journalist. Brig. Gen. Martin Schweitzer, the American commander in eastern Afghanistan at the time, whose troops were involved, also declined to be interviewed.

At first, the meeting to resolve the border dispute seemed a success. Despite some tense moments, the delegations ate lunch together, exchanged phone numbers and made plans to meet again. Then, as the Americans and Afghans prepared to leave, the Pakistanis opened fire without warning. The assault involved multiple gunmen, Pakistani intelligence agents and military officers, and an attempt to kidnap or draw away the senior American and Afghan officials.

American officials familiar with Pakistan say the attack fit a pattern. The Pakistanis often seemed to retaliate for losses they had suffered in an accidental attack by United States forces with a deliberate assault on American troops, most probably to maintain morale among their own troops or to make a point to the Americans they could not be pushed around, said a former American military officer who served in both Afghanistan and Pakistan.

“Looking back, there were always these attacks that could possibly be attributed to deliberate retaliation,” the official said, speaking on the condition of anonymity because his job does not permit him to talk to journalists. Pakistani forces had suffered losses before the May 14 attack, he added.

As with so many problems with Pakistan, the case was left to fester. It has since become an enduring emblem of the distrust that has poisoned relations but is bared only at critical junctures, like Teri Mangal, or the foray by American commandos into Pakistan in May to kill Osama bin Laden, an operation deliberately kept secret from Pakistani officials.

The attack in 2007 came after some of the worst skirmishes along the ill-marked border. By 2007 Taliban insurgents, who used Pakistan as a haven with the support of Pakistan’s military and intelligence establishment, were crossing the border, frequently in sight of Pakistani border posts, and challenging the Afghan government with increasing boldness. American and Afghan forces had just fought and killed a group of 25 militants near the border in early May.

To stem the flow of militants, the Afghan government was building more border posts, including one at Gawi, in Jaji District, one of the insurgents’ main crossing points, according to Rahmatullah Rahmat, then the governor of Paktia Province in eastern Afghanistan.

Pakistani forces objected to the new post, claiming it was on Pakistani land, and occupied it by force, killing 13 Afghans. Over the following days dozens were killed as Afghan and Pakistani forces traded mortar rounds and moved troops and artillery up to the border. Afghanistan’s president, Hamid Karzai, began to talk of defending the border at all costs, said Gen. Dan K. McNeill, the senior American general in Afghanistan at the time.

The border meeting was called, and a small group of Americans and Afghans — 12 men in total — flew by helicopters to Teri Mangal, just inside Pakistan, to try to resolve the dispute. They included Mr. Rahmat. The Afghans remember the meeting as difficult but ending in agreement. The Pakistanis described it as cordial, said Mahmood Shah, a retired brigadier and a military analyst who has spoken to some of those present at the meeting.

The Americans say the experience was like refereeing children, but after five hours of back and forth the Pakistanis agreed to withdraw from the post, and the Afghans also agreed to abandon it.

Then, just as the American and Afghan officials were climbing into vehicles provided to take them the short distance to a helicopter landing zone, a Pakistani soldier opened fire with an automatic rifle, pumping multiple rounds from just 5 or 10 yards away into an American officer, Maj. Larry J. Bauguess Jr., killing him almost instantly. An operations officer with the 82nd Airborne Division from North Carolina, Major Bauguess, 36, was married and the father of two girls, ages 4 and 6.

An American soldier immediately shot and killed the attacker, but at the same instant several other Pakistanis opened fire from inside the classrooms, riddling the group and the cars with gunfire, according to the two senior Afghan commanders who were there. Both escaped injury by throwing themselves out of their car onto the ground.

“I saw the American falling and the Americans taking positions and firing,” said Brig. Gen. Muhammad Akram Same, the Afghan Army commander in eastern Afghanistan at the time. “We were not fired on from one side, but from two, probably three sides.”

Col. Sher Ahmed Kuchai, the Afghan border guard commander, was showered with glass as the car windows shattered. “It did not last more than 20 seconds, but this was a moment of life and death,” Colonel Kuchai said.

As he looked around, he said, he saw at least two Pakistanis firing from the open windows of the classrooms and another running across the veranda toward a machine gun mounted on a vehicle before he was brought down by American fire. He also saw a Pakistani shot as he fired from the back seat of a car, he said. The rapid American reaction saved their lives, the two Afghan commanders said.

The senior American and Afghan commanders had been driven out of the compound and well past the helicopter landing zone when a Pakistani post opened fire on them, recalled Mr. Rahmat, the former governor. The Pakistani colonel in the front seat ignored their protests to stop until the American commander drew his pistol and demanded the car halt. The group had to abandon the cars and run back across fields to reach the helicopters, Mr. Rahmat said.

His account was confirmed by the former United Nations official who talked to the unit’s members on their return that evening.

Those who came under fire that day remain bitter about the duplicity of the Pakistanis. Colonel Kuchai remembers the way the senior Pakistani officers left the yard minutes before the shooting without saying goodbye, behavior he now interprets as a sign they knew what was coming.

He insists at least some of the attackers were intelligence officers in plain clothes.

Mr. Rahmat remains incensed back in Kabul an attack on a provincial governor by Pakistan was quietly smothered. There was never any Afghan investigation into the ambush, for fear of further souring relations.

Official statements from Kabul and NATO went along with the first Pakistani claim insurgents were behind the attack. NATO did not call for an investigation by Pakistan until two days later.

General McNeill, who is retired, remembers the episode as the worst moment of his second tour as commander in Afghanistan, not only because he knew Major Bauguess and his family, but also because he never received satisfactory explanations in meetings with his counterpart, the Pakistani vice chief of army staff, Gen. Ahsan Saleem Hyat.

“Ahsan Hyat did not take it as seriously as me in asking, ‘Have we done as much as we could, and how could we have done it differently?’ ” he said.

Lt. Gen. Ron Helmly, who led the Office of the Defense Representative at the American Embassy in Pakistan at the time, was told the Pakistani soldier who opened fire was unbalanced and was acting alone, yet he was left acutely aware of the systemic shortcomings of Pakistani investigations.

“They do not have a roster of who was there,” said General Helmly, who is retired. “It was all done from mental recollection.” The Pakistani soldiers who fired from the windows consistently claimed they were firing at the Pakistani gunman, he said.

Both Generals Helmly and McNeill accept as plausible a lone member of the Frontier Corps, whether connected to the militants or pressured by them, was responsible, but they also said it was possible a larger group of soldiers was acting in concert. The two generals said there was no evidence senior Pakistani officials had planned the attack.

As for the Afghans, they still want answers. “Why did the Pakistanis do it?” General Same of the Afghan Army said. “They have to answer this question.”