Two top US generals have said they recommended keeping a force of 2,500 troops in Afghanistan, ahead of the full US withdrawal in August, reports BBC.
Testimony by Gen Mark Milley and Gen Frank McKenzie to Congress seemed to contradict President Joe Biden, who said he did not recall any such advice.
The Taliban took power in August, after rapidly advancing through the country.
Gen Milley said the US had been taken by surprise by the speed of the Afghan government's collapse.
The two US generals were questioned by the Senate armed services committee along with Defence Secretary Lloyd Austin on Tuesday.
The hearing comes weeks after a chaotic withdrawal at Kabul airport as foreign powers sought to get their citizens home and thousands of desperate Afghans begged for rescue.
A suicide attack killed 182 people during the withdrawal operation. Thirteen US service personnel and at least 169 Afghans were killed by the airport gate on 26 August.
Keeping troops on the ground
Gen McKenzie, who as head of US Central Command oversaw the withdrawal from Afghanistan, said under questioning from Republican senators that he recommended keeping a small force of 2,500 troops in Afghanistan.
This appears to contradict President Joe Biden's assertion to an ABC journalist on 19 August that he did not recall anyone giving him such advice.
Gen Milley said that he agreed with the recommendation, but when asked by Alaska Republican Dan Sullivan whether Mr Biden's comments were "a false statement", he refused to give a direct answer.
Later White House spokeswoman Jen Psaki addressed the issue.
"The president values the candid advice of... the joint chiefs and the military," she said. "That doesn't mean he always agrees with it."
She said that if troops remained in the country after the August deadline the US would now be at war with the Taliban.
'Caught off-guard'
Tuesday's hearing began with opening testimony from Mr Austin, followed by Gen Milley, who said it would now be harder to protect Americans from terrorist attacks from Afghanistan.
"The Taliban was and remains a terrorist organisation and still has not broken ties with al-Qaeda," he said.
"A reconstituted al-Qaeda or ISIS [Islamic State group] with aspirations to attack the US is a very real possibility, and those conditions to include activity in ungoverned spaces could present themselves in the next 12-36 months."
Gen Milley said he made an assessment in late 2020 that an accelerated troop withdrawal from Afghanistan could precipitate the government's collapse.
But both he and Mr Austin both testified that the speed of the collapse caught the US military off-guard.
"We helped build a state, but we could not forge a nation," Mr Austin said.
"The fact that the Afghan army we and our partners trained simply melted away - in many cases without firing a shot - took us all by surprise."
US troops first entered Afghanistan in late 2001, shortly after the 9/11 attacks. By the time they left, the US had spent about $985bn (£724bn) and deployed tens of thousands of troops, peaking at 110,000 in 2011.
In the weeks between the fall of Kabul and the withdrawal deadline of 31 August, the US evacuated its remaining 4,000 troops. It is also taking about 50,000 Afghan refugees who were airlifted out of Kabul.
As many as 20 people died in the crowds which gathered at the airport in the days after the Taliban takeover.