In a televised address, Biden said he was faced with a choice between sticking to a previously negotiated agreement to withdraw US troops this year or sending thousands more service members back into Afghanistan for a "third decade" of war.

The president said he would not repeat mistakes of the past and did not regret his decision to proceed with the withdrawal.

"I stand squarely behind my decision," Biden said from the White House East Room on Monday.

"After 20 years, I've learned the hard way that there was never a good time to withdraw US forces."

Biden said he would rather take the criticism over the fallout in Afghanistan than leave the decision to another president.

He said the decision to leave Afghanistan was "the right one for America" and keeping a US presence in Afghanistan was no longer a US national security interest.

Biden described the images coming out of Afghanistan - especially at the airport in Kabul, where Afghans descended in hopes of fleeing the country - as "gut-wrenching".

Video of Afghans clinging to a US Air Force plane as it prepared to take off had circulated widely on the internet.

But he did not admit any US fault in how the drawdown was executed. He acknowledged the Taliban takeover unfolded faster than had been anticipated.

About a month ago, Biden batted away the notion of a rapid Taliban takeover.

Biden said the US would continue to support the Afghan people, push for regional diplomacy and speak out for the rights of Afghans.

The speed of the Afghan government's collapse and the ensuing chaos posed the most serious test of Biden as commander in chief, and he came under withering criticism from Republicans who said he had failed.

Biden expressed confidence in his decision to proceed with the withdrawal and said he was prepared to take the heat.

He said he was "deeply saddened by the facts we now face but I do not regret my decision".

Australian Associated Press