Within Shi’ism there is a high level disagreement about the role of Islam in government. Shia-dominated Iran is an Islamic republic, led by Ayatollah Ali Khamenei, a senior Islamic cleric. But the Iranian model of government - a theocratic state - is not supported by Shi’ism’s most senior Islamic cleric, Grand Ayatollah Ali al-Sistani who is based in the Iraqi city of Najaf.

“Khamenei is the head of Iranian army. Sistani is not the head of Iraqi army,” explains Iraqi politician Walid al-Hilli. But, as presenter Safa al-Ahmad discovers on a visit to Iraq, Grand Ayatollah Sistani has significant influence on the way Iraq is governed.

(Photo: A V-sign for victory is flashed in front of a portrait of Grand Ayatollah Ali al-Sistani. Credit: Ahmad al-Rubaye/AFP/Getty Images)