US soldiers killed two armed men at Kabul's airport Monday, according to the Pentagon.

"In the thousands of people who were there peacefully, two guys who had weapons brandished them menacingly. They were both killed," AFP quoted a US defense official, who insisted on anonymity, as saying.

Thousands of US troops took control of security at Afghanistan's main international airport outside Kabul since Saturday to enable the evacuations of US officials.

Afghans, meanwhile, massed at the airport and flooded out onto the tarmac seeking to board commercial flights out of the country.

Earlier, Reuters quoted witnesses as saying at least five people were killed at Kabul airport on Monday when people clung to departing aircraft as they were taking off from the Afghan capital.

Videos showed hundreds impeding a US military aircraft when it tried to take off, and there were reports that several were killed, either being crushed or falling from it after it took off.