U.S. officials say retired Marine Gen. John Allen will coordinate the broad international effort to battle the Islamic State group, as nations begin to determine what part each will play.

Several U.S. officials say Allen will coordinate the contributions of various nations. Nearly 40 countries around the world have agreed to join the fight.

Allen comes to the job with vast experience coordinating international allies on the warfront. He served as deputy commander in Iraq's Anbar province from 2006 to 2008, working with Arab partners on organizing the Sunni uprising against Al Qaeda.

He was the top U.S. commander in Afghanistan from 2011 to 2013, working with international allies.

The officials spoke on condition of anonymity because they were not authorized to discuss the appointment ahead of an announcement.