"I'm here to announce the completion of our withdrawal from Afghanistan and the end of the military mission to evacuate American citizens," said General Kenneth McKenzie, the head of the US Central Command.

The last flight, a large C-17 military transport, took off from Hamid Karzai International Airport one minute before midnight Kabul time, McKenzie said.

On board were US troops, their commander, and US Ambassador Ross Wilson, leaving behind a shuttered embassy that once buzzed with hundreds of diplomats.

It came after an airlift that had evacuated around 123,000 foreign nationals and Afghans fleeing the ultra-conservative Taliban.

The final flight took place under heavy security following two attacks on the two-week evacuation operation by Islamic State-Khorasan -- one a suicide bombing that left more than 100 people dead, including 13 US troops.

Earlier this year, US President Joe Biden set a deadline of August 31 for the withdrawal of US forces from Afghanistan.

Many of the Afghans who were evacuated had worked for the US military and embassy and other countries in the international coalition.

McKenzie said the airlift ended about 12 hours before the final flight and that several hundred US citizens remained behind.

"There's a lot of heartbreak associated with this departure. We did not get everybody out that we wanted to get out," said McKenzie.

"But I think if we'd stayed another 10 days, we wouldn't have gotten everybody out that we wanted to get out."

"There were no evacuees left at the airport," he added.

He said the Taliban had been "very helpful and useful" in conducting the evacuation and keeping security around the airport, despite the deep enmity between the two sides.

"The Taliban have been very pragmatic and very businesslike as we have approached this withdrawal," he said.

US troops led a NATO coalition to eject the Taliban from power in 2001 after the September 11, 2001 attacks on the United States by Al-Qaeda, which was based in Afghanistan and protected by the Taliban.

The sound of gunfire was heard across Kabul after the US military confirmed their exit to end the 20-year war.