The emergency airlift from Kabul of both foreign nationals and Afghans who worked with them is gathering pace as more detail of the desperation and fear driving the rescues emerges.

The US military in Afghanistan sent helicopters to rescue over 150 Americans unable to reach the Kabul airport gates, an official said Friday, in the first evidence that US forces were willing and able to go beyond the US-secured compound to help people seeking evacuation.

The news came as American officials confirmed evacuation operations from Afghanistan stalled for about seven hours Friday, because the receiving base in Qatar was overflowing and could not take in evacuees.

That left thousands more Afghans already cleared to leave their country for the United States waiting at the Kabul Airport.

"It was early this morning, and it lasted about six to seven hours," Major General Hank Taylor told reporters, adding the backlog was subsequently cleared.

The US State Department has been criticized for being overly bureaucratic and not having enough staff to process thousands of Afghans seeking to come to the United States.

Evacuee accounts from Qatar describe sleeping on the floor in sweltering heat in a US aircraft hanger for three days or more, with limited facilities.

Taylor said US aircraft flew some 6,000 people, including a couple of hundred US citizens, out of Kabul in the 24 hours to early Friday, until the bottleneck halted flights.

- Close to the perimeter -

Flights from Kabul resumed late Friday after US operations in Qatar arranged for trips for many evacuees onward to the US military base in Ramstein, Germany.

US citizens and Afghans who worked for the US forces in Afghanistan continued to attempt to get to the airport in Kabul to leave the country.

There were numerous accounts of some struggling to reach and enter the airport, some impeded by Taliban fighters who now control Kabul.

President Joe Biden said Friday that US troops had to go beyond the perimeter of the airport to retrieve 169 Americans, potentially risking a conflict with the Taliban.

Pentagon Spokesman John Kirby downplayed the incident. "They were very close to the perimeter of the airport. Very close," he said, adding later that they had been airlifted from the Baron hotel, near the airport, by three US Chinook helicopters.

The helicopters had been deployed due to concerns for the Americans' safety in traversing a huge crowd that had gathered outside the airport's Abbey entry gate.

"There was a large crowd established outside the Abbey Gate, a crowd that not everybody had confidence in, in terms of their ability to walk through it, and so local commanders on the scene took the initiative and flew these helicopters out there to pick them up," Kirby said.

Taylor said the Taliban have mostly been cooperating with US officials to allow those with US passports or visas to get to the airport and that there was "constant communication" between the US commander on the ground and the Taliban.

"We're seeing that things that we are asking for," such as passage to the airport, "is happening and getting better," he said.

Here is a round-up of the latest developments:

- Biden says evacuation 'difficult', but vows exit -

US President Joe Biden said Friday he could not guarantee the outcome of emergency evacuations from Kabul.

"This is one of the largest, most difficult airlifts in history," Biden said in a televised address from the White House, adding that the US had evacuated more than 13,000 people.

"I cannot promise what the final outcome will be, or... that it will be without risk of loss.

"But as commander in chief, I can assure you that I will mobilize every resource necessary" to conduct a thorough evacuation, he said.

- Reaching airport 'a challenge' - 

Access to the Kabul airport is proving a "big challenge" for foreigners and vulnerable Afghans fleeing the Taliban takeover, warned NATO chief Jens Stoltenberg, who called on the hardline Islamists to let Afghans leave the country.

"We have more planes than we have people or passengers because the process of getting people -- especially Afghans -- into the airport and processed is now the big, big challenge," he said.

- European countries step up -

More than 1,600 people have been brought to safety so far by German armed forces from the Afghan capital, German government spokeswoman Ulrike Demmer said.

A German civilian was wounded by gunfire on his way to the airport, though his life is not in danger and he is to be flown out of Kabul soon, she added.

The German government is planning to deploy two helicopters to support the evacuations, including from "dangerous situations" or to pick people up from remote locations.

The UK said it has evacuated 1,615 people since Saturday -- including 399 British nationals and their dependants, 320 embassy staff, and 402 Afghans.

A Spanish commercial plane carrying 110 people -- mainly Afghans who worked for the Spanish embassy in Kabul and their families -- landed in Madrid Friday afternoon, the government said.

But Defence Minister Margarita Robles said on the radio Friday that one family "lost their daughter in the press of people" as they were boarding the plane, meaning "she stayed in Kabul".

The case showed that "the situation at Kabul airport is simply dramatic," Robles added.

Spain's airbase at Torrejon de Ardoz can house around 1,000 people and will be a hub for Afghan refugees being taken in by EU member states.

Switzerland said it would send a plane to the Uzbek capital Tashkent on Saturday to repatriate Swiss and other evacuees from Kabul. 

Italy said it had evacuated around 1,000 people while more were still waiting at the airport in Kabul.

Some 103 Afghans were due to arrive on Friday night at Rome's Fiumicino airport on a charter plane from Kuwait, it said.

Finland said Thursday it had so far evacuated 34 people, with more Afghan local staff now inside the airport ready to be flown out.

Denmark evacuated around 320 people from Kabul on Thursday, according to the Danish defence and foreign ministers.

Dutch Foreign Minister Sigrid Kaag said a plane with around 180 people aboard is due in the Netherlands later Friday, without giving a breakdown of nationalities.

Kaag said 700 Dutch nationals are still in Afghanistan needing evacuation. The number does not include Afghans who worked for the Netherlands and must be evacuated.

In France, a fourth evacuation plane landed Friday evening carrying around 100 people, 99 of them Afghans, bringing the country's total to more than 550.

- Czech recalls 'demanding' flight -

A Czech army pilot returning from Kabul recalls how there was barely any air traffic control, no refuelling and take-offs "at own risk" in the escape from Afghan capital.

Identified only as "Major M M" on the Czech defence ministry website that published his account of the flight, the pilot brought 62 people to Prague from Kabul on Wednesday.

"I have done a few non-traditional flights, but this one was demanding and damn long," the pilot, who joined the armed forces 20 years ago, said Thursday.

His Airbus carried Czech soldiers, Afghan interpreters and their families, as well as four Afghans whose return had been requested by neighbouring Slovakia.

- Thousands in 24 hours -

The United States airlifted out of Kabul nearly 6,000 people, including a couple of hundred US citizens, in the 24 hours to early Friday, Major General Hank Taylor said.

- Afghan footballer fell to death -

An Afghan footballer who played for the national youth team fell to his death after trying to cling to a departing US plane, the country's sports authority said.

It confirmed the death of Zaki Anwari in the mayhem that erupted at the airport.

- GoFundMe raises millions -

A GoFundMe campaign to raise money for the evacuation of 300 vulnerable Afghans fleeing the Taliban has raised over $6 million, according to figures published Thursday.

The creator of the fundraising page, New York-based Tommy Marcus, asked for funds to organize flights out for Afghans who risk being targeted by the Taliban.