The US might be witnessing a critical week as US officials have warned the country could devolve into a civil war.

A formal conclusion this week to the US military withdrawal, or retrograde, would mark an astonishingly quick end to a process that Biden initiated in April when he ordered the military to leave by September 11, reports CNN.

As many as 1,000 US troops could remain in the country after the formal withdrawal to assist in securing the US Embassy in Kabul and the city's airport, a senior administration official told CNN, and it is now unclear how long NATO troops will remain, the American news channel reported.

A defense official insisted to CNN on Tuesday that the number of US troops in Afghanistan for embassy protection and airport security would not exceed 650 for now.

"This week could be a critical week in the withdrawal and end of the retrograde process," a different defense official told CNN.