Iranian President Hassan Rouhani said Saturday his country is ready to help Iraq if asked, adding that it has “no option but to confront terrorism,” as hundreds of young Iraqi men poured into volunteer centers across Baghdad, answering a call by the country’s top Shiite cleric to join the fight against Sunni militants advancing in the north. 

Dozens climbed into the back of army trucks, chanting Shiite slogans and hoisting assault rifles, pledging to battle the Al Qaeda-linked Sunni group known as the Islamic State of Iraq and the Levant, (ISIS), which has launched a lightning advance across the country.

The massive response to the call by the Iranian-born Grand Ayatollah Ali al-Sistani, issued via his representative Friday, comes as sectarian tensions are threatening to push the country back toward civil war in the worst crisis since U.S. forces withdrew at the end of 2011. 

“Given the current threat facing Iraq, defending the land, honor and holy places is a religious duty,” Ayatollah Sistani said, according to The Wall Street Journal.

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