The US Air Force is investigating human remains found in the wheel well of one of its C-17s that flew out of Kabul amid scenes of chaos resulting from the Taliban takeover of the capital.

In a statement, the air force said that the cargo plane landed at Kabul’s airport on Monday to deliver equipment for the evacuation effort, but it was surrounded by Afghan civilians who had breached the perimeter before the crew could offload the cargo.

“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.

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.

The Air Force did not say how many people died. It said human remains were found in the plane’s wheel well after it landed at al-Udeid Air Base in the Gulf state of Qatar.

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.”