Special report: How Iran's military chiefs operate in Iraq

In particular, Iraqi Shi’ites have grown to trust the powerful Iranian-backed militias that have taken charge since the Iraqi army deserted en masse last summer. Dozens of paramilitary groups have united under a secretive branch of the Iraqi government called the Popular Mobilisation Committee, or Hashid Shaabi. Created by Prime Minister Haider al-Abadi’s predecessor Nuri al-Maliki, the official body now takes the lead role in many of Iraq’s security operations. From its position at the nexus between Tehran, the Iraqi government, and the militias, it is increasingly influential in determining the country’s future.

Until now, little has been known about the body. But in a series of interviews with Reuters, key Iraqi figures inside Hashid Shaabi have detailed the ways the paramilitary groups, Baghdad and Iran collaborate, and the role Iranian advisers play both inside the group and on the frontlines.

Those who spoke to Reuters include two senior figures in the Badr Organisation, perhaps the single most powerful Shi’ite paramilitary group, and the commander of a relatively new militia called Saraya al-Khorasani.

In all, Hashid Shaabi oversees and coordinates several dozen factions. The insiders say most of the groups followed a call to arms by Iraq’s leading Shi’ite cleric Grand Ayatollah Ali al-Sistani. But they also cite the religious guidance of Ayatollah Ali Khamenei, the supreme leader of Iran, as a key factor in their decision to fight and – as they see it – defend Iraq.