His predecessor, Donald Trump, agreed to complete the withdrawal by May 1 in a peace deal struck in February past year.
Meanwhile, dozens of Afghans who worked as interpreters in often deadly conditions with the US military expressed fear on Friday of being targeted by the Taliban after American troops head home, and they urged Washington not to leave them behind.
President Joe Biden applauded his own administration for supposedly "ending the forever war in Afghanistan" during remarks to Congress on Wednesday, despite the fact that he acted to prolong the war beyond the May 1 deadline set by predecessor Donald Trump. Since the start of the war they have taken heavy losses, with estimates ranging from 66,000 to 69,000 Afghan troops killed.
In an exclusive interview with CNN - conducted through intermediaries - two al Qaeda operatives told CNN: "War against the USA will be continuing on all other fronts unless they are expelled from the rest of the Islamic world".
Kabul was braced on Saturday for a reaction from the Taliban, with a visibly increased military presence and security at checkpoints.
"Make no mistake, we have the military means to respond forcefully to any type of attacks against the coalition and the military means to support the (Afghan) security forces", he said. The Pentagon has said it is concerned about personnel coming under attack from the Taliban as they depart so it's not clear if it will disclose all the details of the departure process, which is due to be completed by September 11.
The spokesperson has also hinted that the deal between the Taliban and America might be based on a sham as, al Qaeda claims, the Taliban is not being completely honest with the Biden administration.
Since then contacts have been maintained, official and Taliban sources say, in an effort to try to get the Taliban back to negotiating table and agree to the extended foreign troop presence.
Earlier in the week Mujahid told Reuters conversations were continuing.
The Taliban have previously warned that if foreign troops do not leave Afghanistan within the deadline, the group considers this a violation of the Doha agreement and they will resume attacks on these forces.
"War in Afghanistan was never meant to be a multi-generational undertaking of nation-building", Biden affirmed.
Two of the Western officials said Washington had accepted the Taliban's offer to shield the western military bases from attacks by the likes of Islamic State. "That said, the Taliban is less likely to attack foreign forces now that it knows there is a specific date when they will be leaving". The US and its North Atlantic Treaty Organisation allies went into Afghanistan together on October 7, 2001 to hunt the al-Qaida perpetrators of the 9/11 terrorist attacks who lived under the protection of the country's Taliban rulers.
On Friday, senior Taliban members said they acknowledge Washington's plan, but the delay violates the peace deal. Nor did it have any immediate comment on what the three officials described as a "Taliban ring of protection".
Since the US-led invasion that ousted the Taliban after the September 11, 2001 attacks, America has spent more than United States dollars 1 trillion in fighting and rebuilding in Afghanistan.