A US military investigation into the 2021 Kabul airport blast has concluded that the attack was carried out by a lone suicide bomber.

In a briefing, the head of US Central Command, General Frank McKenzie, said that a so-called Islamic State militant carrying 20 pounds of explosives, detonated himself near one of the airport gates among dense crowds of people.

The blast killed 170 Afghans and 13 US military personnel. 

Probe clarifies initial assessment

Shortly after the attack it was initially reported that there had been two blasts along with accounts of gunfire.

However the investigation has revealed that it was a single blast, and the gunfire was a result of warning shots that were fired by US and British troops shortly after the blast took place.

"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 McKenzie.

Thousands of men, women and children, had descended on the area in a desperate attempt to get onto evacuation flights leaving the country.

The Taliban had just seized control of the capital and many were fearing retribution from the country's new leaders.

Attack was 'not preventable'

According to the lead investigator, the attack could not have been stopped.

"Based upon our investigation, at the tactical level this was not preventable," said Brigadier General Lance Curtis.

McKenzie also pointed out that despite the protective equipment of troops in the area, "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 armor and helmets," which he said did stop impact from ball bearings, but body parts not covered resulted in "catastrophic injuries."

The multinational airlift operation saw around 126,000 people evacuated over the course of around three weeks.

Testimony was gathered from over 100 witnesses, including medical and explosives experts.

Footage from drones and other sources was scrutinized to determine the course of events.

kb/aw (AFP, AP, Reuters)