The war in Iraq has made for some strange bedfellows, namely ex-Sunni Islamic State (ISIS/ISIL) fighters and the Baghdad-sponsored organization of mostly Iran-allied Shiite militias known as the Popular Mobilization Forces (PMF), Foreign Policy (FP) reported this week.

Although the PMF, also known as the Popular Mobilization Units (PMU) and Hashd al-Shaabi, is mostly comprised of Shiites, its members also include Sunni tribesmen, Kurds, Yazidis, and Christians.

The PMF collaborated with U.S.-backed local forces to combat to decimate ISIS’s so-called caliphate in Iraq.

Nevertheless, FP noted on Monday:

The war in Iraq continues to bring together strange partners, and the latest odd couple may be the oddest of all. Particularly in Iraqi territory near Kurdish-held lands, the Popular Mobilization Forces—or the PMF, a collection of mostly Shiite militias—have started to join forces with some ex-Islamic State fighters. The idea of these former foes partnering may seem strange, but there are real benefits for both sides. Factions of the PMF, for their part, get to expand their footprint into Sunni areas. Islamic State fighters, meanwhile, can re-enter Iraqi society. Whatever the end result, it is likely to be bad for Iraq.

The PMF was a key player in the war against the Islamic State that started in 2014. Made up exclusively of Shiite warriors and often fighting under Shiite religious flags, some PMF militias came to be seen as Iranian proxies. That made it difficult for them to work in Sunni-majority areas, and it made the Iraqi government’s international partners, including the United States, suspicious of including them in their own war-fighting efforts.

Like ISIS, some PMF factions have expressed disdain towards the U.S. presence in Iraq, a position that has apparently brought the two groups together.

FP revealed that Ahl al-Haq (AAH) alone, one of the most anti-American PMF groups, has recruited nearly “40 ex-Islamic State” members while the Badr Organization, another faction of the Shiite umbrella organization, recruited 30 others. one of the most radical PMF groups

In November 2017, AAH deemed U.S. troops in Iraq their “enemy,” threatening to attack American forces if they refuse to leave the country.

The Institute for the Study of War (ISW) reported in December 2012 that the PMU’s AAH faction alone claimed responsibility for more than 6,000 attacks on U.S. troops between 2006 and 2011.

On the 17th anniversary of the 9/11 attacks on the U.S. homeland, the White House accused Iranian-backed militias in Iraq of carrying out “life-threatening attacks” against the U.S. consulate in Basra and the U.S. Embassy in Baghdad.

The PMF has been affiliated with U.S.-designated terrorist groups, namely Hezbollah. Republican lawmakers want to sanction militias in Iraq with ties to Tehran to counteract what they see as Iran’s increasing influence in the region.

Baghdad legalized the PMF as a component of the Iraqi military in 2016. Now, the Iran-allied Shiite force is in charge of security in some of the regions taken from ISIS.

The PMF “constitutes a major political force in the country … By all appearances, the PMF would like to expand its writ further. And to do that, it has made a dramatic change in its recruitment strategy. Now, in addition to young Shiites, it is also bringing in ex-Islamic State members,” FP pointed out.

FP acknowledged that AAH denied having ex-ISIS members join its ranks.