WASHINGTON — The United States military has decided that no service members will face disciplinary charges for their involvement in a NATO airstrike in November that killed 24 Pakistani soldiers, an accident that plunged relations between the two countries to new depths and has greatly complicated the allied mission in Afghanistan.

An American investigation in December found fault with both American and Pakistani troops for the deadly exchange of fire, but noted that the Pakistanis fired first from two border posts that were not on coalition maps, and that they kept firing even after the Americans tried to warn them that they were shooting at allied troops. Pakistan has rejected these conclusions and ascribed most of the blame to the American forces.

The American findings set up a second inquiry to determine whether any American military personnel should be punished. That recently completed review said no, three senior military officials said, explaining that the Americans fired in self-defense. Other mistakes that contributed to the fatal cross-border strike were the regrettable result of battlefield confusion, they said.

“We found nothing criminally negligent on the part of any individual in our investigations of the incident,” said one senior American military official involved in the process, who spoke on the condition of anonymity because the results of the review had not been made public.

Mohammad Sajjad/Associated Press

A funeral service in November in Peshawar for soldiers killed in the NATO airstrike. Pakistan has rejected the American findings.

The military’s decision is expected to anger Pakistani officials at a time when the two countries are gingerly trying to patch up a security relationship left in tatters over the past year from a series of episodes, including the shooting of two Pakistanis in Lahore by a C.I.A. contractor, the Navy SEALs raid in Abbottabad that killed Osama bin Laden and the deadly airstrike in November.

Pakistan’s Parliament is scheduled to resume debate as early as Monday on a major review of relations with the United States, a debate that the Obama administration hopes will bring a resumption of full diplomatic relations and the reopening of NATO supply lines into Afghanistan through Pakistan. As part of that debate, Pakistani legislators have demanded an unconditional formal apology from the United States for the fatal airstrike.

In the highest-level parley of leaders of the two countries since the accident, President Obama is to meet with Pakistan’s prime minister, Yousaf Raza Gilani, on Tuesday in Seoul, South Korea, after a nuclear security conference there, to discuss Afghanistan and other security issues. But Mr. Obama is not expected to go beyond the regrets he conveyed to Pakistan soon after the airstrike on Nov. 25.

Some administration aides said at the time that they worried that if Mr. Obama formally apologized to Pakistan, it could provide ammunition for his Republican opponents in the presidential race.

By contrast, Mr. Obama offered a personal apology last month to President Hamid Karzai of Afghanistan for the burning of Korans by American soldiers there, as well as regrets about the massacre of Afghan civilians in which an Army staff sergeant has been charged.

Gen. James N. Mattis, the head of the military’s Central Command, is scheduled to hold long-delayed meetings this week in Islamabad with Gen. Ashfaq Parvez Kayani, the Pakistani Army chief of staff, to discuss the airstrike investigation, as well as new border coordination procedures to prevent a recurrence of the episode.

General Mattis will also discuss opportunities for training, arms sales and improving border coordination centers, military officials said. Other senior American officials, like Deputy Secretary of State Thomas R. Nides, and Marc Grossman, the State Department’s special representative for Afghanistan and Pakistan, are also expected to meet soon with senior Pakistani officials to begin mending relations.

The accidental cross-border attack in November set in motion two inquiries. The first investigation, conducted by the Central Command in December, found that Pakistani troops fired first on a joint Afghan-American patrol, prompting the deadly return fire. That inquiry also concluded that checks and balances put in place to prevent cross-border accidents with Pakistan failed in part because American officials did not trust their Pakistani counterparts enough to give them detailed information about American troop locations in Afghanistan.

That investigation also determined that it took about 45 minutes for a NATO operations officer in Afghanistan to notify a senior allied commander about Pakistan’s calls that its outposts were under attack, one of several breakdowns in communication that contributed to the airstrike.

Once alerted, the commander immediately ordered a halt to the American attacks. By then, communications between the two militaries had sorted out the chain of errors and the shooting stopped. The delay, by at least one officer and possibly a second, raised questions about whether a faster response could have spared some lives.

Officials “did not respond correctly, quickly enough or with the sense of urgency or initiative required given the gravity of the situation and the well-known sensitivity surrounding the Afghan-Pakistan border region,” the December report found.

Pakistan’s military in January issued a withering rejection of the American investigation. It stated that the report was “factually not correct” and that the Americans attacked first; accused the United States of failing to share information “at any level”; and denied any responsibility for the lethal episode.

Pakistan’s generals are likely to be privately angered by the latest American decision, although in public the military is deferring to the parliamentary process. “A full investigation was done by our military, and the conclusions were sent to the parliamentary committee,” said Maj. Gen. Athar Abbas, the military’s spokesman. “Now the government should communicate to the U.S. whatever they want.”

Armed with the information from the first inquiry, the American chain of command in Afghanistan and at the Central Command set out to determine any culpability. They found none that warranted criminal charges, military officials said, nor significant discipline like fines or demotions. It is possible, the officials said, that at some level of the chain of command a soldier could receive an administrative reprimand, but those matters are held privately within the unit or command.

American military legal experts said that the episode illustrated the difficulties of assigning blame when an unintended chain of events results in tragedy.

“The absence of disciplinary action in a specific case doesn’t mean that there was a cover-up or anything like that,” said Charles J. Dunlap Jr., a retired Air Force major general who served as deputy judge advocate general and is now executive director of the Duke University Law School’s Center on Law, Ethics and National Security. “Rather, it may well simply indicate that a tragic accident occurred, and the fog and friction of war make the facts such that assigning criminal responsibility is just not the right thing to do.”

Under orders from General Mattis, American commanders have taken several steps in the wake of the airstrike to prevent such an accident from happening again. These changes include reviewing and harmonizing all directives related to border operations, increased training and coordination, improved surveillance before missions, and more current information on the location of border installations on both sides.

“Cross-border communications have been improved, command levels at border coordination centers have increased, and command relationships have been redefined where needed,” Lt. Col. Jimmie E. Cummings Jr., a NATO spokesman, wrote by e-mail.