The security situation in the Afghan capital Kabul was quickly deteriorating on Sunday after the US embassy issued a security alert over gunfire at the airport.

       Taliban fighters surged into the city after provincial capital after provincial capital fell in the past week.

       The presidential palace has fallen to insurgents and President Ashraf Ghani has fled the country. The militant Islamist group is poised to declare an “Islamic Emirate of Afghanistan”.

       The American flag has been taken down at the US embassy and for the moment, the plan is for a small core of staff, including the top diplomat in the country Chargé d’Affaires Ross Wilson, to remain in a facility at the airport.

       Reuters said there were reports of gunfire as US troops aided evacuation of most other American diplomats and personnel.

       On Sunday, the US embassy said: “There are reports of the airport taking fire; therefore we are instructing US citizens to shelter in place.”

       The New York Times reported that there were at least 10,000 Americans, including Afghan Americans, and Afghan employees who work for the US government who needed to be got out of the country.

       President Joe Biden has authorized the deployment of around 5,000 US troops to Afghanistan to ensure an “orderly and safe drawdown”.

       US military officials said on Sunday that Kabul airport is now closed to commercial flights as military evacuations continue.

       The US is rushing to complete a full withdrawal of its embassy in Kabul within 72 hours as Secretary of State Antony Blinken blamed the Afghan military for “being unable to defend the country”.

       “The fact of the matter is we’ve seen that that force has been unable to defend the country,” Secretary Blinken told CNN’s State of the Union on Sunday. “And that has happened more quickly than we anticipated.”

       He added: “That status quo was not sustainable. Like it or not, there was an agreement that forces would come out on May 1. Had we not begun that process... then we would have been back at war with the Taliban... with tens of thousands of troops.”

       Nato is maintaining its diplomatic presence in Kabul and helping to keep the city’s airport running, the military alliance said on Sunday as Taliban insurgents entered the Afghan capital.

       “Nato is helping keep Kabul airport open to facilitate and coordinate evacuations,” NATO Secretary-General Jens Stoltenberg said on Twitter.

       The Nato chief said that he had spoken with British prime minister Boris Johnson, and the Foreign Ministers of Canada, Denmark and the Netherlands and that the body would help coordinate evacuations.

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       Earlier this summer Nato had withdrawn most troops from Afghanistan after nearly 20 years.

       Reuters contributed to this report