The Pentagon announced Monday that all U.S. troops have departed Afghanistan. The final C-17 carrying service members lifted off from the Kabul airport at 3:29 pm U.S. Eastern Time.

The removal of U.S. troops meets the Aug. 31 deadline the Biden administration agreed to with the Taliban, officially drawing the country's longest-ever conflict to an end.

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But the fate of those left behind remains a mystery, with White House Press Secretary Jen Psaki confirming earlier Monday that a "small number" of Americans who want to leave remain in the country.

Psaki could not give an estimate on exactly how many Americans remained in the country, though a senior State Department official put the number at "below 250."

"There’s a lot of heartbreak associated with this departure," CENTCOM Commander Gen. Kenneth McKenzie said of the closing down of evacuation operations. He acknowledged, "We did not get everybody out that we wanted to get out."

The general added that the ISIS threat to the operation was "very real" until the end, with "overwhelming" U.S. airpower circling overhead in an attempt to prevent further attacks.

In addition to the people left behind in Kabul, McKenzie said the U.S. also left behind equipment such as the C-RAM (counter-artillery, artillery and mortar) system that was used to shoot down rockets, as well as dozens of armored Humvees and some aircraft.

The general added that the equipment had been disabled and in the end none of it was mission capable.