Nato Secretary General Jens Stoltenberg said on Wednesday that the alliance will leave Afghanistan only when security conditions allow, as a deadline for withdrawing troops set out in a peace deal with the Taliban nears.
Nato has just under 10,000 troops helping to train and advise Afghan security forces in the war-torn country.
Most of them are not US troops, but the allies could not continue the Nato operation if American transport, logistics and other support were withdrawn.
President Joe Biden is reviewing predecessor Donald Trump’s 2020 deal with the Taliban, which includes a May 1 deadline for a final US troop pull-out.
In Washington, calls are mounting for the US to delay the departure or renegotiate the deal to allow the presence of a smaller American force focused on intelligence.
Violence from the Taliban, ISIS, warlords and criminal gangs is surging.
“Our presence in Afghanistan is conditions-based and Taliban has to meet their commitments,” Mr Stoltenberg said after chairing a meeting of Nato defence ministers, including new US Defence Secretary Lloyd Austin.
“The main issue is that Taliban has to reduce violence, Taliban has to negotiate in good faith and Taliban has to stop supporting international terrorist groups like Al Qaeda.
“We will only leave when the time is right and the focus now is how we can we support the peace talks.”
He was referring to slow-moving negotiations between the Taliban and the Afghan government, which began last year in Qatar.
None of the 30 Nato member governments has publicly said security conditions are right for a withdrawal, and several allies would probably support a longer stay if the US requested it.
The defence ministers are due to discuss Afghanistan more broadly on Thursday.
But with the US review continuing it is unlikely that any firm decision on the future of Nato’s operation will be made.
That could come when the alliance's foreign ministers next meet, in mid-March.
Nato took control of international security operations in Afghanistan in 2003, two years after a US-led coalition ousted the Taliban for harbouring former Al Qaeda leader Osama bin Laden.
It is the military alliance’s longest, costliest and most ambitious operation ever.