Despite hundreds of thousands of troops from NATO having served in Afghanistan since the September 11, 2001 attacks, last year was the bloodiest on record and the Taliban have made gains across the country.

The Islamist extremists now control more Afghan territory than any time since they were ousted in the US-led invasion of 2001, and once again are imposing their strict interpretation of Sharia law.

Trump is fed up with the war, which has killed more than 2,300 American troops and cost the US taxpayer more than $1 trillion.

The Afghanistan war is "unfortunate, it's ridiculous," Trump said Tuesday in Washington.

In December, he told advisors he wanted to pull about half of America's 14,000 troops out of Afghanistan, a decision apparently made without consulting NATO allies.

But in a ceremony marking at NATO's 70th anniversary at their intensely fortified compound in Kabul on Wednesday, dignitaries sought to put a positive spin on things.

Afghanistan "is a modern and vibrant emerging democracy", said Nicholas Kay, NATO's senior civilian representative in Afghanistan.

"We all salute the improvements in women's rights, for millions of children and notably girls enrolled in schools, the free press and notable advancements in health care," he added.

That narrative is under increasing pressure, however, with the Taliban growing ever stronger and Afghanistan's security forces dealing with horrendous losses.

Last year, a United Nations agency documented 3,804 civilian deaths in Afghanistan, with another 7,819 people injured in the war.

- Tough love -

Kay was joined by Afghanistan chief executive Abdullah Abdullah and NATO's Afghanistan commander General Scott Miller, who championed the alliance's enduring "cohesion".

"We all remain committed to this nation," he said.

Trump, however, has frequently hammered NATO -- accusing longstanding allies of being freeloaders who do not pull their weight on military spending.

NATO Secretary General Jens Stoltenberg has embraced Trump's tough-love approach and credited him with a big increase in member state defence spending.

As for the Afghan gains, many fear America's desire to withdraw from Afghanistan will ultimately see the Taliban back in power.

US special envoy Zalmay Khalilzad is in Afghanistan this week as part of an ongoing drive to find a way out.

He has met with various Afghan politicians and stakeholders, including women representatives, ahead of an expected new round of peace talks with the Taliban in Doha.

Kay insisted NATO is determined to stay in Afghanistan to protect hard-won gains for Afghans.

"We will remain here to assist Afghans until the conditions are right for a change in our posture," he said.