Sattar Jabbar stood at a Baghdad army recruiting station in June wearing nothing but a pair of blue boxer-briefs and a crooked grin. He was waiting for the medical exam required to join Iraq's army, he said, answering a call to arms issued by his spiritual leader, Iraq's senior Shiite cleric.

"I've been trying to volunteer for years, so now I'm seizing the opportunity," he said. "I'm doing this for the Ayatollah Ali Al Sistani and for the prime minister."

At 39 years old, the gray-haired, potbellied father of five doesn't look like the kind of vigorous young man usually sought by armies. But as Sunni militants led by the Islamic State push through Iraq, seizing towns and territory, Baghdad is desperately trying to rebuild its broken army with untrained, mostly Shiite recruits.

The recruitment drive, spurred on by Ayatollah Sistani's religious injunction, is one of Prime Minister Nouri al-Maliki's main solutions for filling the army's porous ranks after thousands of soldiers fled their positions during the Islamist surge that began in June.

Iraq's ability to turn back the militant onslaught, which has gained more ground over the past week, will depend in large part on its ability to bolster its depleted troop ranks and shape a fighting force capable of standing up to the Islamic State.