The United States has formally begun withdrawing its last troops from Afghanistan on Saturday, bringing its longest war nearer to an end, but also heralding an uncertain future for a country in the tightening grip of an emboldened Taliban.

US officials on the ground say the withdrawal is already a work in progress —and May 1 is just a continuation—but Washington has made an issue of the date because it is a deadline agreed with the Taliban in 2020 to complete the pullout.