Shiite, non-Arab Iran has effectively taken charge of Iraq's defense against the Sunni radical group, meeting the Iraqi government's need for immediate help on the ground.
Two to three Iranian military aircraft a day land at Baghdad airport, bringing in weapons and ammunition. Iran's most potent military force and best known general the Revolutionary Guard's elite Quds Force and its commander General Ghasem Soleimani are organising Iraqi forces and have become the de facto leaders of Iraqi Shiite militias that are the backbone of the fight.
The result is that Tehran's influence in Iraq, already high since US forces left at the end of 2011, has grown to an unprecedented level.
Airstrikes by the US-led coalition have helped push back the militants in parts of the north, including breaking a siege of a Shiite town. But many Iraqis believe the Americans mainly want to help the Kurds.
Airstrikes helped Kurdish forces stop extremists threatening the capital of the Kurdish autonomous zone, Irbil, in August. But even that feat is accorded by many Iraqis to a timely airlift of Iranian arms to the Kurds.
A flood of Shiite volunteers joined the fight to fill the void, bolstering the ranks of Shiite militias already allied with Iran.
Those militias have now been more or less integrated into Iraq's official security apparatus, an Iraqi government official said, calling this the Islamic State group's "biggest gift" to Tehran.
"Iran's hold on Iraq grows tighter and faster every day," he said, speaking on condition of anonymity because he was not authorised to discuss the sensitive subject.
