The Islamic State group's takeover of the Iraqi provincial capital Ramadi is prompting criticism from Defense Secretary Ash Carter and raising new questions about the Obama administration's strategy to defeat the extremist group.

The seizure of Ramadi in central Iraq a week ago has revived concerns about U.S. efforts to help fight the group.

The Obama administration's approach in Iraq is a blend of retraining and rebuilding the Iraqi army, prodding the Shiite-dominated government in Baghdad to reconcile with the nation's Sunnis and bombing Islamic State group targets from the air without committing American ground combat troops.

Carter said in an interview aired Sunday on CNN that Shiite-led Iraqi forces did not show a "will to fight" in the battle for the Sunni city.