The plan is for NATO, which runs a 500-strong mission to train Iraqi forces, to take on some personnel and training activities now run by the US-led multinational coalition against the Islamic State group.

But the details -- how many troops will switch and what they will do -- have yet to be worked out because the alliance is still waiting for the Iraqi government's formal agreement.

"Today we have made the decision in principle. We will continue to work on the details and the numbers and exactly what kind of activities," Stoltenberg said.

Spain said it was ready to transfer troops currently working under the aegis of the coalition to the NATO mission, as Western powers seek to enable Iraq to prevent any resurgence of the feared jihadist group.

"We support moving a major part of the Spanish contingent to the NATO mission, while still continuing to work with the coalition," Spanish Defence Minister Margarita Robles said, insisting that any changes must have the backing of the Iraqi government.

Stoltenberg said the alliance wanted to "provide more support to Iraq, because it is extremely important that ISIS never returns.

"We have seen the brutality, have seen the horrendous violence they have been responsible for," he added.

- Munich meeting -

Trump called on NATO to do more in the Middle East in January, days after a US drone strike against a top Iranian commander in Baghdad sparked a regional crisis.

The January 3 strike that killed Iranian General Qasem Soleimani sparked outrage in Baghdad and a vote by the Iraqi parliament to oust all foreign troops -- including 5,200 US soldiers.

The anti-IS coalition halted its campaign for three weeks in response, and NATO stopped training activities while insisting it remained committed to helping Iraq.

British Defence Minister Ben Wallace said London was open to moving some of its troops to the NATO mission, which is seen as more palatable to Iraqi authorities because of its non-combat role and because it is not US-led.

On Friday, Stoltenberg will join a meeting of the global coalition -- which has 11,000 troops across Iraq, Syria and Kuwait -- on the sidelines of the Munich Security Conference, to discuss the planned reconfiguration.

While the NATO mission would do similar training activities to the anti-IS coalition, officials feel the alliance could make it more effective by bringing greater structure and coordination, owing to its experience of training forces in Afghanistan.

Beyond increasing the size of the mission by rebadging coalition personnel, ministers also looked at how NATO could expand its training activities.

This could involve extending geographically outside NATO's current three training zones or adding more training activities.

As a longer-term objective, NATO is looking to see what it could do elsewhere in the Middle East and North Africa to improve stability and fight terrorism by training local forces.

"This is both about military activities, but also political support and cooperation with countries in the region," Stoltenberg said.