The Popular Mobilization Forces (PMF), a largely Shia paramilitary organization under indirect control of the Iranian Islamic Revolutionary Guard Corps (IRGC), have launched an offensive against the Islamic State southwest of Mosul, the Long War Journal reports.

The group’s presence on the battlefield, consisting of thousands of fighters from over 40 separate and predominately Shia militias, has stirred controversy from outside observers who see them as surrogate for Iranian intelligence and special operations influence inside Iraq.

Its operational commander, Abu Mahdi al Muhandis, announced “Operation Mohammed Rasulollah” last Tuesday as part of a series of military operations against the Islamic State in northern Iraq. Muhandis, who was designated a terrorist operative by the United States in 2009, has close ties to the IRGC’s infamous Quds Force Commander Major General Qassem Soleimani.

The PMF is operating without direct assistance from the United States in its joint operation with the Iraqi government to liberate Mosul from the Islamic State. Whether it is purposeful or not, the net effect of American military assistance in defeating the Islamic State currently coincides with the goals of the PMF, which makes many fearful of growing Iranian influence within the Iraqi government under Prime Minister Abadi, and weary of legitimizing the PMF as the world focuses on the threat of the Islamic State.