The mobilisation, urged by the nation's top Shiite cleric, took on a sectarian dimension that threatened to intensify Sunni-Shiite strife in a nation already ripped by religious fervor after the militants' battlefield successes.
In Baghdad, fallout from the stunning advance in the north was beginning to affect daily life for the city's 7 million inhabitants.
The price hikes were partly the result of transportation disruptions on the main road linking the capital with provinces to the north, but they might also be a telltale sign of a nervous city.
"We were not prepared for this sudden spike in the prices of foodstuff, vegetables and fuel," said Yasser Abbas, a government employee from Baghdad's sprawling eastern Sadr City district.
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In the meantime, dozens of men climbed into the back of army trucks at volunteer centers, chanting Shiite religious slogans, hoisting assault rifles and pledging to join the nation's beleaguered security forces to battle the Sunni militants of the Islamic State of Iraq and the Levant, or ISIL.
"By God's will, we will be victorious." said one volunteer, Ali Saleh Aziz. "We will not be stopped by the ISIL or any other terrorists."