The skinny young men in ill-matched uniforms try to march in formation, but struggle to keep in time amid a cacophony of noise from officers shouting orders. “One, two, three!” barks the drillmaster.

The recruits have answered a call by senior Shia clergy, or marjaiyeh, to volunteer for the armed forces to fight against the Islamic State of Iraq and the Levant, the Sunni al-Qaeda splinter group known as Isis.

“I am here because the marjaiyeh call on us to fight Isis,” says 23-year-old Amir Hamza, standing amid a crowd of young men. “Of course my family is scared for me, but ever since the call they have supported me. I have seven brothers and all have signed up.” […]