From across Baghdad, volunteers were ferried in buses to a base in the eastern part of the city for training. In some centers, dozens of them climbed onto the back of army trucks, chanting Shiite slogans and hoisting assault rifles.
"By God's will, we will be victorious," one volunteer, Ali Saleh Aziz, told The Associated Press. "We will not be stopped by the Islamic State of Iraq and al-Sham or any other terrorists."
On Friday, Iraq’s senior Shiite cleric, Grand Ayatollah Ali al-Husseini al-Sistani, issued a call to arms to the faithful in the form of a rare intervention during Friday prayers in the holy city of Karbala.
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"People who are capable of carrying arms and fighting the terrorists in defense of their country ... should volunteer to join the security forces to achieve this sacred goal," said Sheikh Abdulmehdi al-Karbalai, delivering Sistani's message.
Also on Friday, Iraqi television showed extensive clips of Prime Minister Nouri al-Maliki's visit to the holy city of Samarra, home to a much revered Shiite shrine that was bombed in 2006. He declared that Samarra would be the assembly point for the march farther north to drive out the militants, another decision with a religious slant to win over Shiites.
Meanwhile, Iraq's second biggest city, Mosul, fell under Islamic sharia law.
Militants from the al Qaeda offshoot ISIS have decreed that women must wear the veil, and it has outlawed freedom of religion.
It has also banned other armed groups from entering the city.
ISIS fighters, drawing support from former Saddam Hussein-era figures and other Sunnis, have made huge gains in the Sunni heartland north of Baghdad. Soldiers and policemen melted away in the face of the lightning advance, and thousands have fled to the self-rule Kurdish region in northern Iraq.