The Long War Journal is reporting the Mahdi Army's use of Iranian 107 mm rockets, in a crude rocket launching system the US Army calls an IRAM [improvised rocket assisted mortars]. The system is described as a flying improvised explosive device, or airborne IED. The IRAM consists of a large canister, perhaps a propane or fuel tank, filled with explosives and propelled by 107mm rocket booster. According to LWJ, "these types of improvised weapons -- essentially flying IEDs -- would have a short range and would be highly inaccurate". The US military has declared the 107 mm rocket charges to be "of Iranian-manufacture," with lot numbers and dates of manufacture showing that the rocket casings have been manufactured within the past three years.
It should be pointed out that there are better suited weapons in Iranian arms stockpiles to deliver such attacks. The fact that Iraqi Shia militias must go to such extents in fabricating crude delivery systems goes to show that they're not receiving anywhere near optimal weapons support from the Iranians.