The suspected mastermind of a gruesome suicide bombing during the United States' pullout from Afghanistan was killed by the Taliban in recent weeks, U.S. officials disclosed Tuesday, an extraordinary development spotlighting the Biden administration's newfound reliance on a former battlefield adversary to help confront terrorist threats.

An estimated 170 Afghans and 13 American troops died in the 2021 attack near the Abbey Gate at Kabul's airport. Biden administration officials identified the suspect as a leader within the Islamic State's Afghanistan chapter, known as Islamic State-Khorasan or ISIS-K. They declined, however, to reveal the person's name and how the person was killed, citing concerns that doing so could jeopardize the U.S. government's ability to collect information about future activities in the region.

White House spokesman John Kirby characterized the suspect's death as "another in a series of high-profile leadership losses" for the terrorist group. "He was a key ISIS-K official directly involved in plotting operations like Abbey Gate," Kirby said, "and now is no longer able to plot or conduct attacks."

The United States was not involved in the Taliban's operation, according to two other U.S. officials who spoke on the condition of anonymity to discuss sensitive intelligence. The administration, these people said, developed confidence in the assessment only in the last few days. The suspect, they added, was responsible for additional violence in Afghanistan and probably harbored aspirations to carry out attacks on the West.

"I would emphasize that this development represents the continued counterterrorism pressure faced by ISIS-K in Afghanistan and beyond," one of the administration officials said. "We see this operation as emblematic of a landscape in Afghanistan that's become very challenging for terrorists like [those in] ISIS-K, who might want to harm Americans."

Since the U.S. withdrawal, administration officials have maintained that the Taliban, merciless authoritarians, would serve as a check on terrorist activity in Afghanistan - in line with the agreement reached in 2020 to end the war. Approved by President Biden's predecessor in the White House, Donald Trump, the deal stipulated that Afghanistan must never again become a launchpad for attacks on the West. Critics have questioned whether the Taliban could be trusted to meet those obligations and, even then, if its fledgling government could do so effectively.

Kirby said the administration had been clear with the Taliban that "it is their responsibility to ensure that they give no safe haven to terrorists." Tuesday's announcement, he added, "made good on the president's pledge to establish an over-the-horizon capacity to monitor potential terrorist threats, not only from in Afghanistan but elsewhere around the world where that threat has metastasized."

The ISIS bombing on Aug. 26, 2021, occurred in a tightly packed corridor just outside Hamid Karzai International Airport, where - in the aftermath of the Afghan government's stunning collapse to the Taliban - crowds of desperate civilians had massed hoping to board evacuation flights.

U.S. troops who survived the attack have recounted scenes of chaos and carnage, and an abiding frustration with how the operation was managed. The mission relied in part on a hastily arranged agreement in which the Taliban provided security outside the airport while American personnel controlled the airfield itself and oversaw the vetting of Afghans seeking to flee.

The blast wounded dozens of other U.S. troops, some catastrophically, and in the confusion that followed, some believed they were coming under fire from the Taliban. Some shot back and responded incredulously when a Pentagon investigation found last year that the enormous loss of life was caused by a single explosion.

The incident remains one of the lowest moments of the Biden administration, having undercut the president's repeated promises of an orderly end to 20 years of war. Republican lawmakers, vowing accountability for the bloodshed, have held related oversight hearings since reclaiming the House majority this year, placing blame squarely on Biden and his top national security advisers.

The U.S. personnel killed in the Kabul airport bombing include: Marine Lance Cpl. David Espinoza, 20; Marine Sgt. Nicole Gee, 23; Marine Staff Sgt. Darin Taylor Hoover, 31; Army Staff Sgt. Ryan Knauss, 23; Marine Cpl. Hunter Lopez, 22; Marine Lance Cpl. Dylan R. Merola, 20; Marine Lance Cpl. Rylee McCollum, 20; Marine Lance Cpl. Kareem Nikoui, 20; Marine Cpl. Daegan William-Tyeler Page, 23; Marine Sgt. Johanny Rosario, 25; Marine Cpl. Humberto Sanchez, 22; Marine Lance Cpl. Jared Schmitz, 20; and Navy Hospital Corpsman Max Soviak, 22.

The families were notified on Tuesday ahead of a White House announcement.

"It's frustrating because we don't know why they're giving us this information now," Hoover's father, Darin Hoover, said in a telephone interview after he was contacted by a Marine Corps official whom, he noted, provided only vague details about the Taliban's operation.

Hoover questioned whether the White House will take a "victory lap" about the killing and if anyone in the U.S. government will be fired or otherwise held accountable for mistakes made during the evacuation. He expressed disappointment with how senior administration officials have portrayed those events in recent weeks. Defense Secretary Lloyd Austin, he noted, told the House lawmakers in March that he did not have "any regrets" about the operation. He also pointed to comments this month from Kirby, who told reporters at the White House that "I just don't buy the whole argument of chaos."

"It's incredible to me that this is the way they're acting," Hoover said. "It's frustrating, because they're putting the blame everywhere else but on them when it was their operation that did this."

A Pentagon spokesman, Brig. Gen. Patrick Ryder, said Tuesday that Austin does regret the deaths of the U.S. service members. When Austin told members of Congress that he had no regrets, Ryder said, he was referring to the manner with which U.S. troops conducted themselves during the evacuation.

"When it comes to the Gold Star families, we are certainly very empathetic and completely understand how painful this is, and continue to keep them in our thoughts and prayers," Ryder said.

Tuesday's disclosure comes days after The Washington Post reported on classified U.S. military documents that detail an alarming rise in the number of terrorist plots being coordinated by the Islamic State in Afghanistan. Those documents describe ISIS operatives there as having expanded their ambitions to attack the West, even as the Taliban, a sworn enemy, continues to target them.

As U.S. military operations in Afghanistan ended, Biden made the case that the United States did not need to keep American personnel in harm's way in a ground war to launch counterterrorism operations. The United States has carried out strikes against the Islamic State since then in Syria and Somalia, along with a single CIA drone strike in Afghanistan in July that killed Ayman al-Zawahiri, then the leader of al-Qaeda.

But the United States has carried out no known strikes against Islamic State figures in Afghanistan since the U.S. military withdrawal there was completed. Biden administration officials have made the case repeatedly that the Taliban has been an effective counterterrorism force there, carrying out raids on Islamic State hideouts as ISIS operatives continue to target government facilities and ethnic minorities.

"On the Taliban side, they have been very public about their wide-ranging and quite intensive campaign against ISIS-K," one of the senior administration officials said on Tuesday. The United States, he added, is able to conduct attacks there as well "should circumstances warrant."

In March, the top U.S. military commander in the region, Gen. Michael "Erik" Kurilla, warned the House Armed Services Committee that the Islamic State had a stronger presence in Afghanistan than it did a year ago and could be capable of attacks outside the country within six months "with little to no warning." Kurilla added that the United States can see only "broad contours" of the Islamic State's planning there - but not "the full picture."