Nato will significantly increase its troop numbers in Iraq to battle the growing threat from ISIS, Secretary General Jens Stoltenberg said.
The force will increase eightfold, from 500 soldiers mostly based in Baghdad to 4,000, who will be stationed in the capital and bases elsewhere.
The increase is the first in several years and comes after former US president Donald Trump announced that he would reduce US troops from 5,200 to just under 3,000.
It is not clear if President Joe Biden will continue with this reduction given the Nato announcement.
The decision to increase Nato’s presence on the ground was announced by Mr Stoltenberg after a two-hour online meeting of Nato defence ministers.
“Today we decided to expand the Nato training mission in Iraq to support the Iraqi forces to fight terrorism and ensure that ISIS does not return,” he said.
"Training activities will now include more Iraqi security institutions and areas beyond Baghdad.
"Our presence is conditions-based and increases in troop numbers will be incremental.”
Mr Stoltenberg said the mission had been requested by the Iraqi government.
“I spoke with Prime Minister [Mustafa] Al Kadhimi this week and assured him everything will be done in full consultation with the Iraqis,” he said.
Mr Stoltenberg said the country was at a “critical juncture”.
There have been reports, including from senior commanders, that ISIS is recruiting, training and preparing for attacks to try to regain a foothold in Iraq and Syria.
While the terrorist group once controlled an area the size of the UK with a population of eight million people, Mr Stoltenberg said “they have lost that control”.
“But ISIS is still there,” he said. “ISIS still operate in Iraq and we need to make sure they're not able to return.
"We have also seen some increase in attacks by ISIS and that just highlights the importance of strengthening the Iraqi forces.”
It is not yet known which countries will contribute to the mission. Britain has 80 soldiers training security forces in Iraq and could increase its numbers to prepare more Iraqi troops.
“The purpose of the training mission by Nato in Iraq is to prevent the situation when Nato allies may be forced into a situation where they need to be part of the brigade combat operations," Mr Stoltenberg said.
"That is why we are expanding our mission.”
There have been increased rocket attacks on bases in Iraq, many carried out by Iran-backed militias who present a significant threat to stability.
The Nato ministers decided to delay any decision on withdrawing the 10,000-strong force from Afghanistan.
Mr Stoltenberg said this would also be conditions-based, including the Taliban’s adherence to the peace agreement.
Nato members are reluctant to risk undermining progress to democracy as a peace process stalls.
"At this stage, we have made no final decision on the future of our presence," Mr Stoltenberg said.
"As the May 1 deadline is approaching, Nato allies will continue to closely consult and co-ordinate in the coming weeks."
German Defence Minister Annegret Kramp-Karrenbauer said on Wednesday that the Taliban must do more to meet the terms of their 2020 peace agreement with the US to allow a withdrawal of foreign troops.
Attacks in Afghanistan, including a bomb in December that killed the deputy governor of Kabul, have prompted members of the US Congress and international rights groups to call for a delay to the pull-out, agreed on when Donald Trump was president.
"We are faced with many dilemmas and there are no easy options," Mr Stoltenberg said.
"If we stay beyond the first of May, we risk more violence, more attacks against our own troops ... but if we leave, then we will also risk that the gains that we have made are lost."