"We're going to zero troops by September", the source emphasized.
The US says it has some 2,500 troops still in Afghanistan.
Former US President Donald Trump has announced that US troops will be withdrawn by May 1 without consulting allies. There are between 2,500 and 3,500 USA troops in Afghanistan at present.
The official, who spoke to reporters on condition of anonymity ahead of Biden's formal announcement expected on Wednesday, said the president is firm on bringing United States forces to zero by the 20th anniversary of the September 11, 2001, terrorist attacks. "No one wants a forever war, but I've consistently said any withdrawal must be conditions-based".
As the 10-year anniversary of the killing of Osama bin Laden approaches on May 1st, senior USA military leaders have long warned a similar raid would be much more hard without US military troops based in Afghanistan.
Meanwhile, diplomatic efforts to arrive at an intra-Afghan settlement are under way.
The U.S. will help the roughly 7,000 North Atlantic Treaty Organisation troops in Afghanistan pull out of the country under a principle of "in together, out together", the official said.
US Secretary of State Anthony Blinken and US Defence Secretary Lloyd Austin are expected to brief North Atlantic Treaty Organisation allies on the decision in the Belgian capital, Brussels, on Wednesday.
While al-Qaida is not now believed to pose an external threat to the USA, the official said, the country will reposition its counterterrorism assets in the region to monitor and disrupt any potential threats to the homeland. "It is an act of extraordinary political courage and vision", said Rep. Ro Khanna (D-Calif.), a longtime proponent of scaling back military deployments overseas.
"To say I'm concerned is a vast understatement - this is a reckless and unsafe decision", said Sen.
With a firm deadline for departure, US officials are hopeful that the Taliban will not escalate attacks on USA bases and on Afghan security forces in coming months. Jim Inhofe (R-Okla.), top Republican on the Armed Services Committee. "That does not mean we're turning away from Afghanistan".
"We will begin an orderly draw-down of the remaining forces before May 1st and plan to have all USA troops out of the country before the 20th anniversary of 9/11", the official told reporters on a briefing call on Tuesday.
The official warned the Taliban - who are observing a truce with United States but not Afghan forces - not to strike coalition forces as they leave. The roughly 3,500 troops could be airlifted out fairly quickly, but a rushed exit would pose force-protection challenges and necessitate destroying sensitive equipment or leaving it in the hands of the Afghan security forces. The Biden administration has said al Qaeda does not pose a threat to the US homeland now.
As a condition of starting negotiations with the Afghan government, the Taliban also demanded the release of thousands of their men in a prisoner swap.