President Joe Biden is pledging to Americans still trapped in Afghanistan that they will be safely returned to the US.

He said: “We will get you home.”

Mr Biden’s comments at a White House news conference come as the US government struggles to ramp up a massive airlift clearing Americans and other foreigners and vulnerable Afghans through the Kabul airport.

They are being rescued from a Taliban takeover of the country.

Mr Biden is facing criticism for chaotic and often violent scenes outside the airport with crowds struggling to reach safety inside.

He called the past week “heartbreaking,” but insisted his administration was working hard to smooth and speed the evacuations.

“I don’t think anyone of us can see these pictures and not feel that pain on a human level,” Mr Biden said, but “now I’m focused on getting this job done”.

Evacuation flights at the Kabul airport had stopped for several hours on Friday because of a backup at a transit point for the refugees, a US airbase in Qatar, US officials said.

However, a resumption was ordered in the afternoon, Washington time.

As many as three flights out of Kabul were expected in the next few hours, going to Bahrain and carrying perhaps 1,500 evacuees in all, said an official.

In Washington, some veterans in Congress were calling on the Biden administration to extend a security perimeter beyond the Kabul airport so more Afghans can make it to the airport for evacuation.

They also want Mr Biden to make clear an August 31 deadline for withdrawing US troops is not a firm one.

The deadline “is contributing to the chaos and the panic at the airport because you have Afghans who think that they have 10 days to get out of this country or that door is closing forever”, said Peter Meijer, a Republican, who served in Iraq and also worked in Afghanistan to help aid workers provide humanitarian relief.

Tens of thousands of people remain to be evacuated ahead of the United States’ August 31 deadline to withdraw its troops from the country, although the pace had picked up overnight.

A defence official said about 5,700 people, including about 250 Americans, were flown out of Kabul aboard 16 C-17 transport planes.

On each of the previous two days, about 2,000 people were airlifted.

With desperate crowds thronging Kabul’s airport, and Taliban fighters ringing its perimeter, the US government renewed its advisory to Americans and others that it could not guarantee safe passage for any of those desperately seeking seats on the planes inside.

The advisory captured some of the pandemonium, and what many Afghans and foreigners see as their life-and-death struggle to get inside.

It said: “We are processing people at multiple gates.

“Due to large crowds and security concerns, gates may open or close without notice. Please use your best judgment and attempt to enter the airport at any gate that is open.”

While Mr Biden has previously blamed Afghans for the US failure to get out more allies ahead of this month’s sudden Taliban takeover, US officials said American diplomats had formally urged weeks ago that the administration ramp up evacuation efforts.

In July, more than 20 diplomats at the US Embassy in Kabul registered their concerns that the evacuation of Afghans who had worked for America was not proceeding quickly enough.

In a cable sent through the State Department’s dissent channel, a time-honoured method for foreign service officers to register opposition to administration policies, the diplomats said the situation on the ground was dire, that the Taliban would likely seize control of the capital within months of the August 31 pullout, and urged the Biden administration to immediately begin a concerted evacuation effort.

Mr Biden has said that the chaos that unfolded as part of the withdrawal was inevitable as the nearly 20-year war came to an end.

He said he was following the advice of Afghanistan’s US-backed president, Ashraf Ghani, in not earlier expanding US efforts to fly out translators and other Afghans in danger for the past work with Americans.

Mr Ghani fled the country last weekend as the Taliban seized the capital.

Mr Biden also said that many at-risk Afghan allies had not wanted to leave the country.

But refugee groups point to years-long backlogs of applications from thousands of those Afghans for visas that would let them take refuge in the United States.

The administration has also portrayed its contingency planning as successful after the Afghan government fell much faster than publicly anticipated by administration officials.

Yet the White House received clear warnings that the situation was deteriorating rapidly before the current evacuation push.

The Kabul airport has been the focus of intense international efforts to get out foreigners, Afghan allies and other Afghans most at risk of reprisal from the Taliban insurgents.