The head of Iraq's Chaldean Church says that battling extremist "mentality" is key to peaceful coexistence among Iraq's religious and ethnic groups as the nation emerges from more than three years of war with Islamic State militants.

Patriarch Louis Raphael I Sako has told The Associated Press that IS "is done geographically, but it is not done yet ideologically."

However, Sako cautioned that some Muslim clerics are still "spreading hatred" in the country by labelling Christians as "infidels" in their sermons.

Iraqi Christians number around 500,000 today, down from 1.5 million more than a decade ago.

When the Islamic State group blitzed across western Iraq in 2014, thousands of Christians fled. The extremists would force Christians to convert to Islam or pay a special tax, and often confiscated their property.