Top Shiite cleric Grand Ayatollah Ali al-Sistani called Friday for Iraqis to take up arms against "terrorists" who have overrun swathes of the country in a major offensive.
"Citizens who are able to bear arms and fight terrorists, defending their country and their people and their holy places, should volunteer and join the security forces to achieve this holy purpose," his representative announced on his behalf during Friday prayers in the city of Karbala.
"He who sacrifices for the cause of defending his country and his family and his honour will be a martyr," he added.
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The elderly Sistani, who rarely appears in public, is highly influential in the Shiite Muslim world and is adored by millions.
An offensive launched by the Sunni Islamic State of Iraq and the Levant and its allies late Monday has overrun all of one province and chunks of three more.
Security forces have so far failed to halt the drive, with some fleeing after throwing away their uniforms and abandoning their positions.
Shiite Prime Minister Nuri al-Maliki has already announced that the government will arm and equip citizens who volunteer to fight.