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 that 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 that 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 that 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 that 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.