Video on social media showed hundreds of people running alongside the huge craft and clambering onto it as it rolled along a runway and what appears to be at least two Afghans plummeting from an airborne C-17 transport.
The US Air Force said that it is investigating the circumstances surrounding human remains that have been found in the wheel well of one of its C-17s that flew out of Kabul amid the chaos of the Taliban taking over the Afghan capital.
Images circulated on social media earlier this week of Afghans desperate to leave Kabul rushing toward a C-17 and clinging to its side. A separate video showed what appeared to be two people falling from a military plane as it flew out of Kabul.
In a statement, the Air Force said that a C-17 aircraft landed at Kabul's airport on Monday and was surrounded by hundreds of Afghan civilians.
"Faced with a rapidly deteriorating security situation around the aircraft, the C-17 crew decided to depart the airfield as quickly as possible," the statement said.
It added that the Air Force's office of Special Investigation was reviewing information about the aircraft and the "loss of civilian lives - to include video documentation and the source of social media posts."
Over 600 Afghans crammed into US cargo plane
More than 600 Afghan men, women and children, crouching and crammed up against each other on the floor of a US military plane, left Kabul.
A photograph showing the Afghan civilians - some clutching luggage, others bottle-feeding infants - on the C-17 cargo aircraft has gone viral on social media.
A US official told Reuters about 640 people clambered onto the flight from Kabul on Sunday, when thousands of people desperate to flee the country surged to the airport in the Afghan capital.
"The unusually high number of passengers was the result of a dynamic security environment that necessitated quick decision making by the crew which ultimately ensured these passengers were quickly taken outside the country," the official said.
According to the manufacturer, Boeing, the C-17 Globemaster III can carry 134 passengers, including 54 on side seats and 80 on pallets on the floor.
New aviation milestones!!— Shantanu Nandan Sharma (@shantanunandan2) August 17, 2021
US evacuated some 640 Afghans from Kabul, to Qatar on Aug 15.
Possibly the most people ever flown in C-17 military cargo plane. pic.twitter.com/pBOgyjBWCM
Taliban's rapid takeover
The Taliban's rapid conquest of Kabul followed US President Joe Biden's decision to withdraw US forces after 20 years of war - the nation's longest - that he described as costing more than $1 trillion.
The speed at which Afghan cities fell, in days rather than the months predicted by US intelligence, and fear of a Taliban crackdown on freedom of speech and human rights, especially women's rights, have sparked criticism.
In a televised address on Monday afternoon Biden defended his decision, blaming the Taliban's takeover on Afghan political leaders who fled the country and the Afghan army's unwillingness to fight.