NATO Secretary General Jens Stoltenberg has warned the alliance could pay a heavy price for withdrawing troops from Afghanistan "too soon".
It comes after a US official said President Donald Trump is expected to bring home a considerable number of American troops in the coming weeks.
Mr Stoltenberg said: "We now face a difficult decision. We have been in Afghanistan for almost 20 years, and no NATO ally wants to stay any longer than necessary.
"But at the same time, the price for leaving too soon or in an uncoordinated way could be very high."
The alliance's chief said the conflict-devastated nation "risks becoming once again a platform for international terrorists to plan and organise attacks on our homelands".
"And ISIS [so-called Islamic State] could rebuild in Afghanistan the terror caliphate it lost in Syria and Iraq," he added.
Just days ago, President Trump appointed officials in top Pentagon positions who share his frustrations over continued troop presence in the war zones.
The expected plans would cut US troop numbers almost in half by mid-January, leaving 2,500 troops in Afghanistan.
According to US officials, military leaders were told over the weekend about the planned withdrawal, and that an executive order is being prepared but has not yet been delivered to commanders.
NATO took control of the international security effort in Afghanistan in 2003, two years after the US-led coalition ousted the Taliban for harbouring former al-Qaeda leader Osama bin Laden.
The alliance started to train and advise Afghan security forces in 2014, but has gradually pulled personnel out, in conjunction with a US-brokered peace deal.
NATO has a heavy reliance on the US military to operate in Afghanistan.
According to the British Army's website, there are nearly 1,000 UK troops deployed in Afghanistan.
Last month, soldiers from 2nd Battalion The Royal Regiment of Scotland began deploying to Afghanistan as part of NATO's Resolute Support mission, taking over from sister battalion, 4 SCOTS.
Cover image: Library photo of Jens Stoltenberg (Picture: NATO).