US President Joe Biden on Tuesday defended his decision to pull American troops out of Afghanistan and said it was in the US national interest to do so.

"We no longer had a clear purpose in an open-ended mission in Afghanistan," he said in a speech, a day after the final US plane left Kabul.

"This is the right decision. A wise decision. And the best decision for America," he stated.

Biden stated that the US airlift of more than 120,000 people from Afghanistan was an "extraordinary success".

"We completed one of the biggest airlifts in history," the President said, adding, "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 pledged to help the scores of US citizens who remain in Afghanistan to leave the country.

"For those remaining Americans, there is no deadline. We remain committed to get them out if they want to come out," Biden said.

He also had a message for Islamic State-Khorasan, the terrorist group which claimed last week’s suicide bombing at Kabul airport, in which 13 US troops were killed.

"We will maintain the fight against terrorism in Afghanistan and other countries. And to ISIS-K: We are not done with you yet," warned Biden.