"Not all 200 are US citizens. There are American citizens amongst the group departing Kabul to Doha," said the source, who was briefed on the operation.

Footage broadcast by Qatar's Al Jazeera TV showed families including women, children and elderly people waiting with suitcases at Kabul airport.

"We are very appreciative of the Qataris," one passenger told the channel, giving his nationality as Canadian.

The United States has said that only 100 or so US citizens remain in Afghanistan, but that thousands of Afghan allies who fear retribution failed to leave before the departure of the US military last week.