A 2021 suicide bombing in Kabul that killed scores of people -- among them 13 American troops -- could not have been prevented "at the tactical level," according to the findings of a supplemental US review released Monday.

The review -- which was detailed by members of the team that conducted it -- confirmed the conclusions of a previous US investigation into the August 26, 2021 Abbey Gate bombing.

The attack targeted crowds of people on the perimeter of Kabul airport who were desperate to get on a flight out of the country as the Taliban took power in the closing days of the American withdrawal from Afghanistan.

It left more than 170 people dead.

"There was no opportunity to engage the bomber prior to the attack," which "was not preventable at the tactical level," a review team member told journalists on condition of anonymity.

The bomber arrived "very shortly before the attack," and was not the "suspicious individual" identified by snipers earlier in the day of the bombing, the review team member said.

Another member of the review team said that "over the past two years, some servicemembers have claimed that they had the bomber in their sights, and they could have prevented the attack. But we now know that is not correct."

The findings contradict the account of ex-Marine sergeant Tyler Vargas-Andrews, who was wounded in the bombing and has insisted that an opportunity was missed to stop it.

The supplemental review was launched last year in light of the discovery of previously undisclosed information in statements by Vargas-Andrews, and because other wounded servicemembers were not interviewed due to their evacuation after the attack, the US Central Command said at the time.

The Abbey Gate bombing was claimed by the Islamic State jihadist group, and the White House said last year that the Taliban killed the mastermind of the attack.

The US withdrawal saw Taliban fighters sweep aside Afghan forces, forcing the last American troops to mount an evacuation from Kabul's airport that got more than 120,000 people out of the country in a matter of days.

US President Joe Biden has long defended the decision to leave Afghanistan, which critics have said helped cause the catastrophic collapse of Afghan forces.

That paved the way for the Taliban to return to power two decades after their first government was toppled by American troops.