The operation involved several unmanned U.S. aircraft, and it struck a vehicle in which Mansour was traveling. A second passenger, whom officials described as another combatant, was also probably killed, the official said, but a final assessment has not yet been made.

Pentagon press secretary Peter Cook, announcing the airstrike in a statement, said Mansour had posed a danger to U.S. and Afghan forces and to local civilians and had disrupted U.S.-backed ­efforts to broker a political solution to Afghanistan’s long conflict.

“Mansour has been an obstacle to peace and reconciliation between the Government of Afghanistan and the Taliban, prohibiting Taliban leaders from participating in peace talks with the Afghan government,” Cook said.

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A senior Afghan Taliban commander told the Associated Press early Sunday that Mansour was killed in the attack. Mullah Abdul Rauf told the news agency that Mansour died in the strike late Friday night “in the Afghanistan-Pakistan border area.” U.S. officials have not confirmed Mansour’s death, but Afghanistan’s National Directorate of Security, as the secret service is known, said in a statement Sunday that he was killed at 3:45 p.m. on Saturday.

If confirmed, Mansour’s death would be a significant development as Afghan government troops, backed by a small contingent of U.S. and partner forces, prepare to take on an emboldened Taliban during what is expected to be a punishing summer fighting season.

Officials said it was too soon to say what the death of Mansour, who emerged as the Taliban chief in summer 2015, would mean for that fight.

Mansour took on the public mantle as Taliban leader after the news broke that Mohammad Omar, the movement’s iconic longtime chief, had died in 2013.

While Mansour, who had been an aide to Omar and a Taliban transportation minister, prevailed in the initial succession struggle after Omar’s death, he faced significant rivalries within Taliban ranks and, in a sign of the scale of those fissures, was said in unconfirmed reports to have been shot during a meeting of militants late last year.

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At the same time, U.S. and coalition officials have been surprised at how quickly he managed to overcome internal divisions within the group. Mansour repeatedly rebuffed outreaches from Pakistan and elsewhere that the Taliban enter into peace talks with the Afghan government.

Instead, according to U.S. and Afghan military officials, he called on the Taliban to fight at least through this year to see whether the group could maximize its strategic bargaining position. Mansour also infused the leadership of the Haqqani network, which the United States considers a terrorist group and which for years operated as a somewhat independent offshoot of the Taliban, into his command structure.

In recent weeks, Brig. Gen. Charles H. Cleveland, chief spokesman for coalition forces in Afghanistan, has stated that Sirajuddin Haqqani, who was named Mansour’s top deputy, has been taking a leading role in planning battlefield strategy.

Andrew Wilder, vice president of Asia programs at the U.S. Institute of Peace and a longtime Afghanistan expert, said that Mansour’s death would be unlikely to have a major effect on the level of violence in Afghanistan.

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“You could see some factional fighting that could take some pressure off the government, but in general, I don’t think it’s going to lead to a significant reduction in the fighting,” he said. “I think any successor is going to use the fight against the government to unify Taliban factions around [his] leadership.”

That will have implications for the U.S. military mission in Afghanistan. With about 9,800 troops on the ground, the U.S. presence is far smaller than it was at the height of Obama’s troop surge and is now more narrowly focused on advising Afghan forces and fighting al-Qaeda, rather than battling the Taliban.

But that focus has become more difficult to maintain as the Taliban has grown stronger across Afghanistan and threatened the stability of the U.S.-backed government in Kabul. As local forces have grappled with repeated Taliban offensives, U.S. commanders have sought to provide vital support, raising questions about whether the United States can shift away from the Taliban fight.

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“The United States may not be at war with the Taliban, but that doesn’t mean that the Taliban and especially its most senior leadership isn’t continuing to target U.S. and partner forces and facilities, and isn’t very destabilizing for Afghanistan’s future, which also threatens U.S. interests,” said Ambassador Daniel F. Feldman, who was Obama’s special representative for Afghanistan and Pakistan until last year.

The ongoing insecurity has also prompted Obama, who came into office promising to end the long wars launched by his predecessor, to delay his withdrawal plans several times.

In Pakistan, Foreign Ministry spokesman Nafees Zakaria said, “I have seen the reports. We are seeking clarification. I reiterate Pakistan’s principled position that the Taliban must give up violence and come to the negotiation table as called for by the QCG [Quadrilateral Coordination Group]. I also reiterate that military action is not a solution.”

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The American strike in Baluchistan, outside the tribal regions where most U.S. air attacks have taken place, may introduce a new note of tension into U.S.-Pakistani ties.

According to the Long War Journal, which tracks airstrikes in Pakistan, this is the first time the United States has been reported to have conducted a strike in Baluchistan. All but two of its 392 strikes in Pakistan have taken place in the tribal regions along Pakistan’s border with Afghanistan.

When Mansour was initially appointed, most analysts thought that Pakistan’s military and intelligence had pushed for him to be named as Omar’s replacement. But Mansour’s resistance has proved to be a major obstacle to peace talks, which Pakistan’s military and government have supported.

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Pakistani leaders and analysts had begun to quietly tell U.S. diplomats and journalists that they no longer had the leverage over the Taliban that they did in the past. While it was hard to document the veracity of those statements, it appeared that frustration was also building in Islamabad over the Taliban’s refusal to join talks.

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It’s not clear who may assume leadership of the Taliban and whether the organization will solidify or fracture after Mansour’s death. Designating Haqqani as leader, for example, could signify a hardening of the Taliban’s reluctance to enter peace talks.

But Feldman said Mansour’s death may bring a new possibility. “I would hope that his death, once confirmed, would signal to the Taliban that there’s a new opportunity to engage in good-faith reconciliation efforts,” he said. “That type of negotiated political settlement is what we’ve always said this conflict would require for long-term resolution.”