KABUL (AFP) - A huge international airlift of foreigners and Afghans who worked with them continued on Tuesday (Aug 17) as thousands of people terrified at the prospect of Taleban rule flocked to Kabul airport.

Nato Secretary-General Jens Stoltenberg said the alliance would send additional aircraft to bolster the operation after member states met on Tuesday, adding that evacuations were "gradually resuming" following chaotic scenes on Monday after commercial flights were halted.

In addition to aircraft, the US has sent military reinforcements to protect the exodus, with troop numbers swelling to 4,000 on Tuesday.

Major-General Hank Taylor, a top military official, said the US aimed to increase its airlift to one aircraft an hour so that between 5,000 and 9,000 passengers could be carried out per day.

"We are confident we have taken the right steps to resume safe and orderly operations at the airport," he said.

The United States "has the responsibility and the means" to evacuate Afghans who helped Washington in Afghanistan, former US President George W. Bush, who launched the US offensive in the country 20 years ago, said on Tuesday.

The US plans to evacuate more than 30,000 people by plane from Kabul to its military bases in Kuwait and Qatar.

Washington said on Tuesday the Taleban had promised safe passage for civilians wanting to leave via the airport.

"The Taleban have informed us they are prepared to provide the safe passage of civilians to the airport, and we intend to hold them to that commitment," National Security Adviser Jake Sullivan told White House reporters.

The US was also "talking" with the Taleban about the timetable for the removal of thousands of American citizens and Afghans fleeing the country on US military aircraft, he said.

He added that President Joe Biden has not spoken with fellow world leaders since Kabul fell.

"He has not yet spoken with any other world leaders," Sullivan said.

"Myself, Secretary (Antony) Blinken, several other senior members of the team have been engaged on a regular basis with foreign counterparts and we intend to do so in the coming days."

Afghans crammed on plane

A staggering 640 Afghan men, women and children crammed inside one Air Force C-17 Globemaster transport plane as they fled Kabul on Sunday, according to a report by a US defence analysis website, which published a picture that went viral.

Such a large number of passengers was not expected on a single flight, a senior US official told the website Defense One, but many desperate people had clambered inside at the last moment through the half-open ramp at the back of the plane.

"The crew made the decision to let them in," rather than to force them back down, the official said.

Some other countries, including Germany and France, have also been able to land aircraft to pick up their nationals and Afghans qualified to travel to those countries.

A first French plane, with 45 French nationals and Afghans aboard, arrived at Paris Charles de Gaulle airport on Tuesday.

Sweden announced that all its diplomatic personnel had returned home.

Taleban 'hindering' exodus

Germany accused the Taleban of blocking would-be refugees from reaching Kabul airport, amid an operation to evacuate some 10,000 Afghans who have worked with the German military or NGOs.

A German military plane that landed in Kabul overnight Monday managed to leave with only seven people on board.

"The Taleban have set up checkpoints everywhere in the city and have the entire area and the airport surroundings in their hands," German Foreign Minister Heiko Maas told reporters.

The only people allowed through into the airport are "foreign citizens, but no local workers and no Afghan citizens" are given access, he said.

Thousands of panicked people fled to the airport in a bid to get on departing Western flights, after the Taleban seized control of Kabul.

Austria and Romania have also indicated that their nationals and the Afghans they intend to evacuate are experiencing difficulties in reaching the airport.

Madrid has sent two planes to Dubai from Zaragoza to repatriate its embassy, nationals and Afghans who worked with Spain, the defence ministry said.