A military investigation into the deadly attack during the Afghanistan evacuation has concluded that the deaths of more than 170 Afghans and 13 US service members were not preventable.

A suicide bomber, carrying 20 pounds of explosives packed with ball bearings, acted alone to carry out the strike at Abbey Gate outside the Kabul airport on August 26, the probe found.

At the Pentagon on Friday, military officials laid out a minute-by-minute account of the bombing that killed 11 US Marines, a sailor and a soldier, who were screening the thousands of Afghans trying to board flights leaving the country after the Taliban takeover.

The bottom line, the officials said, was that those who died had wounds that were "so catastrophic” that they couldn't be overcome. 

They said that earlier thoughts that it was a complex attack involving gunfire turned out to be unfounded.

Daesh had claimed responsibility for the attack.

“A single, explosive device killed at least 170 Afghan civilians and 13 US service members by explosively directing ball bearings through a packed crowd and into our men and women at Abbey gate,” said Gen. Frank McKenzie, head of US Central Command.

“The disturbing lethality of this device was confirmed by the 58 US service members who were killed and wounded despite the universal wear of body armour and helmets that did stop ball bearings that impacted them, but could not prevent catastrophic injuries to areas not covered.”

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Chaos and destruction

Investigators said the bomber likely got near the gate by bypassing Taliban and other security checkpoints.

They said it appears the Taliban didn't know of the attack, that security precautions were being taken, and that intelligence about potential threats circulating that day was not specific.

Brig. Gen. Lance Curtis, who led the investigation, said military leaders on the ground in Kabul followed proper security measures.

Military officials said the gunfire after the blast was found to be warning shots fired by US and British troops, and that no one was killed or wounded by gunshots.

Friday's briefing lasted more than an hour and resembled the detailed explanations military officials gave to the families of the troops killed that day. It included several videos of the chaos at the gate at the time of the bombing.

Investigators said as the Taliban made it more difficult to get through checkpoints, Afghans and others began using side roads and back alleys to get closer to the outer gate.

The investigation also concluded that there was enough medical staff and blood at several sites around the airport, including nine surgical teams and a hospital.

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