WASHINGTON: US Secretary of State Antony Blinken said on Sunday that embassy staff in Kabul are leaving the facility and moving to the airport, as Taliban insurgents entered the Afghan capital and an official said President Ashraf Ghani had left for Tajikistan.

US diplomats were being ferried by helicopters to the city's airport, where US troops are being flown in to provide security amid an exodus of Americans and their local allies and other foreigners in the face of the militants' lightening advance.

Sources told Reuters that most US staff would be evacuated from Kabul in the coming day or two.

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"We're working to make sure that our personnel are safe and secure. We're relocating the men and women of our embassy to a location at the airport," Blinken said.

More US forces had been sent in to get US officials out of the country "in a safe and orderly fashion" while maintaining a "core diplomatic presence," Blinken added.