The Hashd al-Shaabi – Iraqi paramilitary forces known as the Popular Mobilization Forces – captured an air base from the Islamic State on Thursday, the Iranian media reports. According Iranian outlets affiliated with the Islamic Revolution Guards Corps (I.R.G.C.), the seizure of the Sahl Sinjar airbase, which is about 40 miles east of the Syrian border, provides the P.M.F. forces a “strategic foothold” in western Mosul and helps them to push further toward the Syrian border. Fars News Agency, an I.R.G.C. mouthpiece, said the paramilitary forces have also seized control of several areas in Qairawan and Sinjar regions in western Mosul. Harakat al-Nujaba, an Iran-supported unit within the P.M.F., is reportedly playing a leading role in military operations against the Islamic State in Qairawan.

Comment: While the Iraqi security forces are preparing to liberate the strategic city of Tal Afar from the Islamic State, Iran-backed Shiite militia forces have launched a parallel operation – dubbed Muhammad Rasulullah – in western Mosul. The aim of the operation, now in the second phase, is to seize all strategic regions between western Mosul and Iraq’s border with Syria. That will provide the I.R.G.C. strategic supply lines to and from Syria. On the Syrian side, the I.R.G.C.-led forces and the Syrian Army have are also pushing forward to reach the border region. Reuters reported yesterday that P.M.F. Head Falih al-Fayyadh met with Syrian President Bashar al-Assad in Damascus on Thursday and discussed "close and direct" military cooperation against the Islamic State along the shared border. Some P.M.F groups – such as Harakat al-Nujaba and Asaib Ahl al-Haq – are already fighting in both Iraq and Syria under the direction of I.R.G.C. Quds Force Commander Qassem Soleimani.

The P.M.F. forces launched the Muhammad Rasullah operation on April 25 and have so far captured several regions from the Islamic State, including the historic city of al-Hadar in western Mosul. The P.M.F. has also begun a joint offensive with the Iraqi army to retake areas between the provinces of Diyala and Salahuddin.

The P.M.F.’s leading role in military operations in western Mosul – particularly the prominent role of Iran-backed units within the P.M.F. – has caused a great deal of concern for Iraqi Sunnis and some regional Sunni states. It is feared that some sectarian groups within the P.M.F. might engage in revenge killing and rights abuses against Sunnis in western Mosul once the Islamic state is defeated. Jawad al-Talibawi, a spokesman for the armed wing of Iran-controlled Asaib Ahl al-Haq, revealed earlier this week that P.M.F. “forces will not participate in the upcoming operation to liberate the city of Tal Afar “due to pressure by Turkey, America and some other countries” which he accused of supporting the Islamic State. However, Talibawi stressed that P.M.F. forces will instead lead another offensive to seize areas in western Mosul all the way to the Syrian border.

The P.M.F. consists of militia forces largely from Shiite but also other Iraqi ethnic and religious groups. While some P.M.F. units are Iraqi nationalists and follow Iraq’s top cleric Grand Ayatollah Ali Sistani, many prominent groups within P.M.F. have close ties with Qassem Soleimani, the head of the I.R.G.C.’s elite Quds Force. What makes Sunnis particularly worried is that, despite P.M.F.’s diversity, it is the Iran-backed militia units within the P.M.F. – such as Asaib Ahl al-Haq, Kata’ib Hezbollah and the Badr Organization – that are playing the most prominent role in western Mosul. These groups have also launched a vicious propaganda campaign against U.S. troops advising Iraqi forces in Mosul and across Iraq.