In a statement, it gave no specifics but made clear that the focus now will be on consolidating military gains made against IS after more than three years of fighting in Iraq and Syria.

"2018 will be a critical year in adjusting coalition forces as it consolidates gains against Daesh and brings hope for a better future to the Iraqi people," it said using the Arabic acronym for IS.

The coalition had previously announced its intention to reduce its presence but not so clearly as in Monday's statement.

Several weeks ago, US Defense Secretary Jim Mattis said the mission would change from taking territory from IS to one of stabilization.

The coalition, created in 2014 in response to an IS offensive across northern Iraq, today has 74 countries as members as well as international organizations like NATO and Interpol.

Brigadier General Jonathan Braga, the coalition's director of operations, said "an appropriate amount of capabilities" would be kept in Iraq in addition to the forces needed to train, advise and equip the Iraqis.

"We're clear the enemy is still capable of offensive action and retains the ability to plan and inspire attacks worldwide," he said.

But the focus will shift to policing, border controls and building up military strength, he said.

The United States has deployed about 2,000 soldiers in Syria and more than 5,000 in Iraq.

At the end of November, it announced the withdrawal of 400 Marines from Syria, while also deploying 3,000 reinforcements to Afghanistan.