Asked if he had a message for the public as he walked towards a plane, one purported Taliban member said, "My message is to have no worries. Everything is going fine."
Forced into a hasty and humiliating exit, Washington and its NATO allies carried out a massive but chaotic airlift over the past two weeks, but still left behind tens of thousands of Afghans who helped Western countries and might have qualified for evacuation.
Celebratory gunfire rang out in Kabul after completion of the U.S. pullout that ended America's longest war.
Taliban spokesman Qari Yusuf said: "The last U.S. soldier has left Kabul airport and our country gained complete independence," Al Jazeera TV reported on Monday.
A contingent of Americans, estimated by U.S. Secretary of State Antony Blinken as under 200 and possibly closer to 100, wanted to leave but were unable to get on the last flights.
President Joe Biden, in a statement, defended his decision to stick to a Tuesday deadline for withdrawing U.S. forces even though it meant not everyone who wanted out could get out.
Biden has drawn heavy criticism from Republicans and some of his fellow Democrats for his handling of Afghanistan since the Taliban took over Kabul earlier this month after a lightning advance.