Emboldened by a call to arms by the top Shiite cleric, Iranian-backed militias have moved quickly to the center of Iraq’s political landscape, spearheading what its Shiite majority sees as a fight for survival against Sunni militants who control of large swaths of territory north of Baghdad.

The emergence of the militias as a legitimate force enjoying the support of the Shiite-led government and the blessing of the religious establishment poses a threat to Iraq’s unity, planting the seed for new sectarian strife and taking the regional Shiite-Sunni divide to a potentially explosive level.

Iraq’s Shiite militias attacked U.S. forces during the eight-year American presence in the country. They also were in the lead in the Sunni-Shiite killings of 2006-07, pushing Iraq to the brink of civil war. Their death squads targeted radical Sunnis and they orchestrated the cleansing of Sunnis from several Baghdad neighborhoods.

More recently, Shiite militias have been battling alongside the forces of President Bashar Assad and Lebanon’s Shiite Hezbollah against mostly Sunni rebels and militants in neighboring Syria. Some of them have returned home to Iraq — first to fight Sunni militants in Anbar province, and now on Baghdad’s northern fringes and in Salahuddin and Ninevah provinces.

Those are the areas where the Sunni militants from the Islamic State of Iraq and the Levant, or ISIL, captured cities and towns in a lightning offensive last week. Among their gains were Mosul, Iraq’s second-largest city, and Tikrit, the hometown of Saddam Hussein.

Security officials said Shiite militiamen have been fighting for months on the government’s side against ISIL fighters in areas west of Baghdad in mainly Sunni Anbar province as well as parts of Diyala province northeast of the capital. They also have been fighting Sunni militants south of Baghdad. Their involvement, however, has never been publicly acknowledged by the government of Prime Minister Nouri al-Maliki.

Their enhanced role in the fight against the Sunni militants will deepen Iran’s influence in Iraq, giving the non-Arab and mostly Shiite country a role similar to the one it plays in Syria. Tehran has thrown its weight behind Assad’s government in his struggle against mostly Sunni rebels and militants from al-Qaida-inspired or linked groups.

Shiite militiamen interviewed by The Associated Press in the past two days talk of undergoing training in Iran and then being flown to Syria to fight on the government’s side. Once there, they say they are met by Iranian operatives who give them weapons and their assignment.

The militiamen, interviewed separately, paint a picture of their groups as being inspired by what they call a “grave” threat to their community. They say they have been motivated by the call to arms by their most revered cleric, the Iranian-born Grand Ayatollah Ali al-Sistani.

Ominously, they don’t see the ISIL as their sole enemy; they also list Iraqi Sunnis whom they accuse of supporting the al-Qaida-inspired group in areas now under the militants’ control.

Their comments also suggest a high level of acquiescence by al-Maliki’s Shiite-led government. Six years ago, the government battled the Shiite militias in Basra to establish his authority and project his image as a national leader.

Now, al-Maliki publicly meets with militia leaders, like Qais al-Khazali of the Iranian-backed Asaib Ahl al-Haq, or League of the Righteous, a group that staged some spectacular attacks against U.S. troops before their withdrawal in 2011.

Hadi al-Amiri, a Shiite Cabinet minister who once led the Badr Brigade militia, created by Iran and trained by its Revolutionary Guard in the 1980s, is now a close ally of al-Maliki and personally directs battles against militants in Diyala province northeast of Baghdad, where he won a parliament seat in April elections.

After years of repeated assurances that the Badr Brigade had ceased to exist as a militia, bearded men in military uniform bearing its insignia appeared on state-run TV last week, standing shoulder-to-shoulder with army troops.

The militiamen and their leaders offer a glimpse of what may be in store following the fighters’ public empowerment.

“Anyone who supports or sympathizes with the ISIL is a terrorist,” Abu Wareth al-Moussawi, a spokesman for the Iraqi al-Nugabaa militia, told the AP from Iran. “We will never allow ISIL to control Iraq, and we will target anyone who supports it.”

Jassim al-Jazaeri, a senior leader of the Iranian-backed Hezbollah Brigades, a Shiite militia based in southern Iraq, blames the loss of territory in the north partially on Sunni political leaders. “We know that ISIL has a base of support in Mosul,” he said.

Since al-Sistani made his call to arms Friday through a representative, Shiite militias have flexed their muscles on the streets of Baghdad and in cities across the mostly Shiite south, including Basra. There were parades of pickup trucks carrying armed fighters chanting Shiite slogans and vowing to crush the ISIL.

Radical and anti-American Shiite leader Muqtada al-Sadr, whose Mahdi army fought some street battles against the Americans, has called for parades of Shiite militiamen across Iraq next weekend, evidence of their empowerment.

“The defense of Iraq and its people and holy sites is a duty on every citizen who can carry arms and fight terrorists,” said al-Sistani’s representative, Sheik Abdul-Mahdi al-Karbalaie, in a Friday sermon. “They must volunteer in the security forces for this holy cause.”

His call quickly resonated with Shiites, who wait on every word from al-Sistani or his representatives. It was instantly used by the militias to tout their legitimacy and flex their muscle on the streets.

Authorities looked the other way while the militiamen paraded on the streets since Friday, but the shows of strength prompted al-Sistani’s office to issue a clarification late Saturday, warning against “any behavior that has a sectarian or a nationalist character that may harm the cohesion of the Iraqi people.”

It also called for a halt to armed displays “outside legal frameworks” in mixed Shiite-Sunni area, urging authorities to take measures to stop them.

The words from al-Sistani’s representative on Friday, warning that the Sunni militants would not stop until they reach Baghdad, Karbala and Najaf — home to some of the most revered Shiite shrines — provided the militias with religious cover. The protection of shrines was also the rallying cry of Iraqi Shite militiamen who traveled to Syria to fight Sunni rebels.

“I fight for my faith, country and holy sites,” said Ayad al-Rubaei, a 23-year-old Asaib Ahl al-haq militiaman and veteran of the Syrian civil war.

“It is martyrdom that I seek, and I want it today, not tomorrow,” al-Rubaei told the AP by phone from Anbar province as heavy gunfire rang out in the background.

Prominent Sunni lawmaker Salim al-Jubouri told the AP that the shows of force by the Shiite militias and their proliferation “will pose a grave danger to Iraq in the future and threaten an armed conflict.”

“We say ‘no’ to the ISIL and ‘no’ to the militias,” he said.

(AP)