WASHINGTON - President Joe Biden on Monday 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.

Biden said the mission of the United States was never supposed to be nation building as he blamed the Taliban's takeover of Afghanistan on Afghan political leaders who fled the country and the unwillingness of the Afghan army to fight the militant group. "I stand squarely behind my decision," 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," Biden said.

The Democrat has faced a barrage of criticism, from even his own diplomats,  over his handling of the US exit, pulling out troops and then sending back thousands to help with the evacuation.

Thousands of civilians desperate to flee Afghanistan thronged Kabul airport's single runway on Monday after the Taliban seized the capital, prompting the United States to suspend evacuations.

Five people were reported killed in the chaos. A US official told Reuters two gunmen had been killed by US forces there over the past 24 hours.

Biden also said his decision is a result of the commitment he made to American troops that he wasn't 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 criticized but I would rather take all that criticism than pass this decision on to another president."

Biden also coupled his defense with a warning to Taliban leaders: let the US withdrawal proceed unimpeded or face devastating force.

Reuters