WASHINGTON (REUTERS/AFP) - US President Joe Biden on Monday (Aug 16) said he "stood squarely behind" his decision to withdraw US troops from Afghanistan and rejected broad criticism of the chaotic withdrawal that is posing a crisis for him.

"I am president of the United States of America and the buck stops with me," Mr Biden said in a much-awaited televised address from the White House, after several days of silence on the momentous developments.

Mr Biden said the mission of the US was never supposed to be nation building as he blamed the Taleban's takeover of Afghanistan on Afghan political leaders who fled the country and the unwillingness of the Afghan army to fight the militant group.

As scenes of mayhem unfolded in the Afghan capital, Mr Biden said he was "deeply saddened" by the turn of events - and promised to "speak out" on the rights of women now facing a return to Taleban rule.

But he was steadfast in insisting he did not regret pulling out America's troops - despite a torrent of criticism of the chaotic end to two decades of US-led military intervention.

"I stand squarely behind my decision," Mr Biden said. "After 20 years I've learned the hard way that there was never a good time to withdraw US forces. That's why we're still there."

"The truth is: This did unfold more quickly than we anticipated. So what's happened? Afghanistan political leaders gave up and fled the country. The Afghan military gave up, sometimes without trying to fight," Mr Biden said.

The President also said his decision is a result of the commitment he made to American troops that he was not going to ask them to continue to risk their lives for a war that should have ended long ago.

"Our leaders did that in Vietnam when I got here as (a) young man. I will not do it in Afghanistan," he said. "I know my decision will be criticised but I would rather take all that criticism than pass this decision on to another president."

And the US President issued a stark warning to the Taleban not to disrupt or threaten the evacuation of thousands of American diplomats and Afghan translators at the Kabul airport.

"We will defend our people with devastating force if necessary," he said.

Frustration grows

Frustration and anger at Mr Biden's handling of evacuations from Afghanistan are mounting among administration officials, lawmakers of both parties and advocacy groups.

As US diplomats hunkered inside, thousands of desperate Afghans thronged Kabul airport, where five people were killed on Monday, prompting the US military to temporarily suspend flights to clear the airfield.

Five US officials, speaking on condition of anonymity, told Reuters that, weeks before the Washington-backed Afghan government collapsed, the US military wanted a bigger role in helping to evacuate Afghans at risk because they worked for the US.

The officials believe that a more orderly withdrawal would have been likely. "We could have done a lot more to help. The administration waited too long," a military official said.

In response, a senior administration official cited comments on Monday by National Security Adviser Jake Sullivan, who said Mr Biden's team has been "engaged for months of extensive scenario planning and was ready for this challenge".

Despite the government's rapid collapse, Mr Sullivan said the embassy was closed "safely and swiftly" and that, "we are now laser-focused on getting people out safely and swiftly".

There were also issues with the intelligence, with one assessment last week saying Kabul would not be isolated for the next 30 days at least.

A source familiar with the situation said the Biden administration was behind the curve as things deteriorated in Afghanistan. "Every decision has come too late and in reaction to events that make the subsequent decision obsolete," the source said.

Local embassy employees who have been at home for weeks were left to make their own way to the airport, the source said, adding that e-mails were sent to them on Sunday after sporadic gunfire to remain in their houses or some other safe location.