First US troops have started leaving Afghanistan as Biden decides not to extend withdrawal deadline

"So far, the reduction does not affect the mission," one of the officials said, adding that the commander on the ground can decide what military personnel are in units that are no longer required. That decision can be based on a few factors, including the number of gates open at the airport, the number of people coming through and more.

"If you can have a smaller mission set and still conduct the mission, then you can reduce your footprint and reduce your risk," the official said.

The Pentagon has been acutely aware of the threat posed by ISIS-K and other terror groups around the airport, developing alternate routes to the field for US citizens and Afghan evacuees. In addition, the Taliban have stated openly that they do not want a US military presence in Afghanistan beyond the end of August, warning that there will be "consequences" were the US to stay longer.

In remarks to an emergency meeting of the G7 on Tuesday, Biden said the threat to US troops in Kabul was one of the key reasons he was sticking to the end of the month as the final withdrawal date.

"There has been no change to the timeline of the mission, which is to have this completed by the end of the month," Pentagon press secretary John Kirby said Tuesday morning.

"If the worst-case scenario were to happen, you don't want more people there than you need," the defense official said.

As the US nears the final date of withdrawal, the number of Afghan evacuees flown out is expected to gradually decrease, while the number of US troops flown out is expected to increase.

This story is breaking and will be updated.

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