Biden defends US pullout from Afghanistan as Taliban celebrate

President Joe Biden on Tuesday (31) mounted a fierce defense of his exit from Afghanistan as the "best decision for America," the day after the US military withdrawal celebrated by the Taliban as a major victory.

"This is the right decision. A wise decision. And the best decision for America," Biden said in an address to the nation in Washington, after he stuck to an August 31 deadline to end two decades of bloodshed that began and ended with the hardline Islamists in power.

He spoke after the United Nations warned of a looming "humanitarian catastrophe" in Afghanistan, underscoring the daunting challenges that the victorious Taliban face as they transform from insurgent group to governing power.

For America, Biden argued, the only choice in Afghanistan was "leaving or escalating."

And the president, whose critics have savaged him for his handling of the withdrawal, said the frenzied airlift -- which saw the United States and its allies fly more than 120,000 people fleeing the new Taliban regime out of Afghanistan -- was an "extraordinary success."

"No nation has ever done anything like it in all of history; only the United States had the capacity and the will and ability to do it," he said.

The Taliban also saw the airlift as a success: a mark of their astonishing comeback and defeat of a global superpower.

Taliban fighters fired weapons into the sky in Kabul in the early hours of Tuesday in jubilation after the last US plane flew out. Later, they swept into the capital's vast airport.

"Congratulations to Afghanistan... this victory belongs to us all," Taliban spokesman Zabihullah Mujahid told reporters hours later on the airport runway.

Mujahid said the Taliban's victory was a "lesson for other invaders".

In Kandahar, the spiritual birthplace of the movement and the country's second-largest city, thousands of celebrating supporters swept onto the streets.

- 'Darkest hour' -

All eyes will now turn to how the Taliban handle their first few days with sole authority over the country, with a sharp focus on whether they will allow free departure for those wanting to leave -- including some foreigners.

The US has said that "under 200" of its citizens remained in the country, and Britain said the number of UK nationals inside was in the "low hundreds."

Thousands of Afghans who worked with the US-backed government over the years and fear retribution also want to get out.

Talks are ongoing as to who will now run Kabul airport, which German chancellor Angela Merkel warned was of "existential importance" as a lifeline for aid.

Many Afghans are terrified of a repeat of the Taliban's initial rule from 1996-2001, which was infamous for their treatment of women and girls, as well as a brutal justice system.

The group has repeatedly promised a more tolerant brand of governance compared with their first stint in power, and Mujahid persisted with that theme.

"We want to have good relations with the US and the world. We welcome good diplomatic relations with them all," he said.

Mujahid also insisted Taliban security forces would be "gentle and nice".

But UN chief Antonio Guterres gave a stark assessment of the challenges they face as they build their new regime.

He expressed his "grave concern at the deepening humanitarian and economic crisis in the country," adding that basic services threatened to collapse "completely."

He pleaded for financial support from the international community for the war-ravaged country, which is dependent on foreign aid.

"I urge all member states to dig deep for the people of Afghanistan in their darkest hour of need," Guterres said in a statement.

- 'Not done' with IS-K -

Authorities from several countries have already begun meeting with Taliban leadership, the latest being India.

Qatar's foreign minister, Sheikh Mohammed bin Abdulrahman al-Thani, urged the Taliban to combat terrorism after the US withdrawal, and called for an inclusive government.

Some Afghans also appealed to the Islamist movement to keep its promise of a softer rule.

Fawzia Koofi, a rights activist and former negotiator for the ousted government who has twice survived assassination attempts, called on the Taliban via Twitter to include all Afghans as they turn to ruling.

"Taliban, hear us out: we must rebuild together!" she wrote. "This land belongs to all of us."

Other activists struggled to find hope.

"If I let my thoughts linger on what we have lost, I will lose my mind," Muska Dastageer, who lectured at the American University of Afghanistan, said on Twitter.

The US-led airlift began as the Taliban completed an astonishing rout of government forces around the country and took over the capital on August 15.

The withdrawal came just before the August 31 deadline set by Biden to end the war which began with the US invasion in the wake of 9/11 -- a conflict that claimed the lives of tens of thousands of Afghans and more than 2,400 American service members.

The slightly early finish came amid a threat from the regional offshoot of the Islamic State group, rivals of the Taliban, to attack US forces at the Kabul airport.

Thirteen US troops were among more than 100 people killed late last week when an IS suicide bomber attacked the perimeter of the airport, where desperate Afghans had massed in the hope of boarding an evacuation flight.

Biden said Tuesday that the United States would continue the fight against terrorism in Afghanistan and other countries, and warned IS: "We are not done with you yet."