The promise came at the at the end of a meeting of NATO defence ministers whose second and final day was largely focused on the 16,000-strong deployment in Afghanistan as it grapples with increased Taliban attacks and uncertainty over US strategy.

US President Donald Trump has already unnerved allies by abruptly pulling US forces out of northern Syria this month, opening the way for NATO member Turkey to launch a disputed operation to crush the Kurdish militias it regards as "terrorists".

That situation dominated the first day of the meeting.

Trump also created waves last month on Afghanistan by scuppering a secret summit with Taliban leaders and Afghan President Ashraf Ghani that was meant to consider a draft deal under which the US could withdraw its thousands of troops.

NATO Secretary General Jens Stoltenberg presented an unruffled position on Afghanistan, saying: "NATO remains committed and we continue to support the Afghan forces."

He added that, while the US-led NATO deployment would be "constantly adjusted," its continued presence was needed "to send a message to the Taliban that they need to compromise" to reach a peace deal.

He also stressed that the situations in Syria and Afghanistan were "two totally different things," as NATO was not involved in Syria.

- Chinese conference -

China is seen stepping into the diplomatic void created by the US on Afghanistan.

It has invited a Taliban delegation to an "intra-Afghan" conference in Beijing being held next Tuesday and Wednesday, a spokesman for the militants, Suhail Shaheen, told AFP this week.

The Taliban refuse to talk to the Afghan government, and Shaheen said any attendance by Afghan officials in Beijing would be on the understanding they were representing only themselves and were low-ranked.

Beijing has not confirmed the conference, but says it is "willing to facilitate" the Afghan peace process.

The United States has not reacted to the alleged Chinese move.

But the US State Department on Thursday urged restraint as Afghans wait for results from September 28 elections.

Preliminary results have been delayed for what Afghanistan's electoral authorities said were technical issues. The last polls in 2014 were marred by allegations of rigging.

Days ahead of the election, the Trump administration cut $160 million in direct funding to Afghan authorities, citing corruption.

- 5G scrutiny -

At the NATO meeting, US Defense Secretary Mark Esper drove home Washington's assessment of "the threat a more assertive China presents to the alliance," more so than Russia or Iran.

While it was not clear the extent other allies shared that view, part of the two-day meeting was given over to NATO members updating "baseline requirements" for introducing 5G telecoms networks.

Esper said he made plain his country's objections to allies using Chinese company Huawei, a cost-effective pioneer in the 5G roll-out, stressing that "the alliance relies on secure communications for intelligence-sharing and military mobility".

Stoltenberg said the baseline update was part of NATO's scrutiny of sensitive civilian infrastructure and was necessary because, in terms of telecoms, "the old guidelines didn't address 5G at all" and cyberattacks and dangers from foreign ownership or control of networks had grown.

He said that the revision was "not about a specific country or a specific company" but more about establishing "requirements that all allies have to meet".