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The Iraqi government announced an operation to clear the Islamic State (IS) out of Fallujah on the evening of 22 May. In the intervening three weeks, IS have lost numerous villages and towns around Fallujah and Iraqi counterterrorism forces are to have entered Fallujah proper in the south.

As the first major city IS took on its way to proclaiming a caliphate in June 2014, the pace of the operation is not the most troubling element. What is disturbing - and what may ultimately undo any military success against IS - is the overtly sectarian nature of the offensive, led not by professional troops loyal to Baghdad, but by militias loyal to Iran and the extremist ideology of Tehran's clerical regime.

As in previous offensives against IS-held cities in Iraq that are led by Iran's Islamic Revolutionary Guard Corps (IRGC), notably Tikrit in early 2015, there was a great deal of obfuscation initially about the role of the militias, for reasons of political sensitivity.

After Mosul fell to IS in June 2014, an umbrella structure was set up, al-Hashd al-Shabi, for the (largely Shia) volunteers to assist the government after the army collapsed. The volunteer mobilisation and the Hashd were quickly co-opted by Iran.

The most powerful elements within the Hashd are pre-existing radical sectarian Shia militias - the Badr Corps, Kataib Hizballah, Asaib Ahl al-Haq (AAH) and innumerable offshoots - loyal to Iran's Supreme Leader. They are run by the Quds Force, the expeditionary wing of the IRGC commanded by , a twice-designated terrorist. The Quds Force, working through these proxy militias, was used by Tehran to kill Western soldiers and participate in sectarian atrocities, including mass ethnic cleansing in Baghdad, during the occupation of Iraq.

The US does not want to be seen as providing air support to Iranian proxy militias, and came up with a workaround that is now referred to as the "Tikrit rules"

The formal second-in-command of the Hashd is Jamal Ebrahimi (Abu Mahdi al-Muhandis), who is also . Ebrahimi is Suleimani's deputy and leads Kataib Hizballah, which is a .

The US does not want to be seen as providing air support to Iranian proxy militias, and came up with a workaround that is now referred to as the "". The IRGC-led forces in Tikrit were bogged down and needed US air power to complete the operation, so the militias ostensibly retreated from the frontlines and handed command to the Iraqi government.

The US then the airstrikes that allowed the completion of IS's expulsion from Tikrit. As it happens, the militias didn't pull back in anything but name, but even if they had, the Federal police were involved in Tikrit, as they , and the Badr Corps controls the Interior Ministry and has heavily infiltrated their ranks.

Moreover, the militias openly moved in afterward, against "collaborators", and taking control of the city, which they maintain to this day. The militia's role in Fallujah is much more extensive and deep-rooted than Tikrit.

Iran mobilised its Iraqi proxies in late summer and autumn of 2012 to participate in the in support of Bashar al-Assad's regime in Syria. A year later, they began flowing back into Anbar during the attack ordered by then-Iraqi Prime Minister Nouri al-Maliki against a burgeoning insurgency.

Al-Maliki's raid of a protest camp in Ramadi in December 2013 triggered a full-scale uprising that IS quickly hijacked, and Fallujah had fallen within days. Every to retake the town since then has been carried out by IRGC-controlled militias. Fallujah has been under near-constant attack since IS took over, often in that violate the laws and customs of war.

IS has prevented people from leaving Fallujah and its opponents have imposed a near-total siege. The last food delivery in the area was in September 2015, and was . By early 2016, it was that the 50,000 civilians remaining in Fallujah were short of food. By April 2016, it was that 140 people had died of starvation.

The displacement of IS by IRGC-run extremist groups and the US shift toward an alignment with Iran across the region is bringing IS exactly what it wants

Within a week of the Fallujah offensive beginning, the images and videos started circulating on social media of the militias' crimes: tortured prisoners, beheaded captives and desecrated corpses.

Accompanying this were the sectarian provocations. These included the display of Iranian flags, the Iranian Basij forces chanting sectarian slogans on the outskirts of Fallujah, the of Ayyub al-Rubaie (Abu Azrael) - the axe-wielding, who fronts one of Iran's militias - and the appearance of Suleimani and Ebrahimi themselves around Fallujah.

None of this began in the last month. The from the leader of one of Iran's militias that this offensive was "our chance to clear Iraq by eradicating the cancer of Fallujah," was only the latest such remark to display genocidal intentions.

and have documented an incident in the town of Saqlawiya, about five miles from Fallujah, which the militias took from IS on 2 June, where 1,250 Sunni military-age males were taken into custody. About half of them were released on 5 June with visible marks of torture and there are reports that four men had been killed by the militias' brutality.

Days before this, according to "several" members of the Hashd itself and a local villager, Hashd militiamen had "stabbed dozens of villagers to death with knives".

HRW has also reported other incidents. In al-Karma, about 10 miles from Fallujah, which fell to the militias a few days after the Fallujah offensive began, 70 men and boys are still missing, likely in the hands of the militias. Seventeen male residents of nearby Sajar were separated out from a crowd of civilians and massacred.

The Salafi-jihadists are now able to present a more convincing narrative that their way is the only way to Islamist rule

One notable, immediate effect of this is that it has heaped discredit on Sunni leaders who supported the government offensive. This is particularly true of the Muslim Brotherhood's Iraqi Islamic Party, which might be thought of as a posthumous victory for the , Abd al-Rahman al-Qaduli. His hatred for the Brothers' "deviant" methodology - namely trying to transform society by engagement with the governing regime, rather than its violent overthrow - now has a much wider audience. 

In combination with the , the Salafi-jihadists are now able to present a more convincing narrative that their way is the only way to Islamist rule.

In the medium-term the Fallujah operation has complicated the liberation of Mosul. It is likely there will be wide-scale destruction in Fallujah to evict the to IS jihadists - as happened in Ramadi.

IS has, in previous operations against cities its caliphate in Iraq, either allowed the civilian population to flee or been unable to stop them. In Fallujah however, IS has embedded in a civilian population it has held hostage. Given the penalties inflicted on those who flee by both IS and the militias, many Fallujans will opt to stay.

Given the penalties inflicted on those who flee by both IS and the militias, many Fallujans will opt to stay

Facing a stark choice between IS's rule or the destruction of their cities followed by sectarian persecution from militias run by a foreign state, it is not difficult to foresee Sunnis choosing the former, if only to protect their homes and families.

Over the longer term, the displacement of IS by IRGC-run extremist groups and the US shift an alignment with Iran across the region is bringing IS : The chance to fulfil a and pose as the sole defender of the interests and security of Sunni Arabs against an international conspiracy consisting of the West, Russia and Iran, working through Arab Shia proxies.

Under these conditions, IS's "defeat" - the loss of senior leaders and its control of cities - will be ephemeral; merely the prelude to a .

Kyle Orton is a Middle East analyst and an associate fellow at the Henry Jackson Society. Follow him on Twitter:

Opinions expressed in this article remain those of the author and do not necessarily represent those of °®Âþµº, its editorial board or staff.