Iraqis from Ramadi flee toward Baghdad. (Hadi Mizban/AP)

The capital of Anbar province fell to Islamic State militants Sunday as hundreds of police personnel, soldiers and tribal fighters abandoned the city, prompting the Iraqi premier to order Iranian-aligned Shiite militias to join the fight to win back control.

The fall of Ramadi represented a huge victory for the Islamic State and dealt a profound blow to Iraq’s U.S.-backed government, led by Prime Minister Haider al-Abadi, and its military campaign to drive the extremist group out of the war-torn country. Just 24 hours before, officials in Baghdad announced that military reinforcements had been dispatched to defend the city, in Iraq’s largest province, against a brutal assault that began Thursday.

But by Sunday, even the roads to Baghdad, 80 miles to the east, appeared vulnerable to the militant advance.

“Ramadi is now entirely under the control of Daesh,” said Ahmed al-Salmani, a member of parliament who represents Anbar province. Daesh is the Arabic acronym for the Islamic State.

Sunday’s developments, including Abadi’s decision to deploy Shiite militias to the country’s Sunni heartland, could complicate the U.S.-led campaign targeting the extremist group, which in recent days has included American airstrikes against militant positions in Ramadi. U.S. officials have expressed concern over the divisive and increasingly powerful Iranian-backed Shiite militias.

Abadi’s announcement on state television Sunday evening, which contained few details, also included a plea for pro-government forces not to abandon their positions in Anbar.

The rapid disintegration of pro-government forces in Ramadi conjured memories of the Islamic State’s similar rout of Iraq’s weak military during sweeping advances throughout northern areas of the country last summer.

Security forces retreated from the Malaab area of Ramadi at 1:30 p.m., abandoning about 60 military vehicles, including military-grade Humvees, said Col. Nasser al-Alwani of the Ramadi police force. About half of the abandoned vehicles were sent by the U.S.-backed government on Saturday to reinforce the neighborhood, he added.

The force of about 400 police officers under Alwani’s command also retreated in their vehicles to the east, he said. Islamic State fighters besieged them on every road, forcing them to abandon the vehicles and escape on foot. A military convoy from the al-
Habbaniyah air base later retrieved the fleeing Iraqi forces, he added.

“The retreat was complete chaos. There was no organization,” Alwani said, describing attacks by “hundreds” of Islamic State militants.

Earlier in the day, militants posted an Islamic State statement on social media that described Sunday’s events as a major military success, saying that the group “had imposed its control over all of Ramadi.”

In Mosul, Iraq’s second-largest city, which the Islamic State has controlled since June, fighters fired automatic weapons into the air and passed out candy in an impromptu street celebration, according to a resident in the city. He spoke on the condition of anonymity, citing concern for his safety.

“The streets are full of cars honking horns and shouting Allahu Akbar because of Ramadi,” he said in a Facebook message.

The prime minister’s order to Shiite militias came hours after Anbar’s provincial council voted in favor of allowing the irregular forces — known by the government as “popular mobilization units” — to participate in the battle to retake the city.

“We took this decision because we have nowhere else to turn. We’ve literally lost everything,” said Kahtan Abed, assistant to the provincial council’s head, Sabah Karhout.

Iraqis, particularly in Sunni-dominated Anbar, are wary of the militias and the Shiite-led government in Baghdad, the capital. The Islamic State has capitalized on Sunni grievances to take control of most of Anbar.

Diplomats, analysts and some Iraqis say that the militias threaten to undermine Iraq’s government as well as delicate sectarian relations in the country. With aid from Shiite Iran, the militiamen carried out scores of attacks against American soldiers during the Iraq war. But more recently, the militias have proved to be a crucial force in retaking territory, including the city of Tikrit last month, from the Islamic State.

An official in one of the Shiite militias, Kitaeb Hezbollah, confirmed by text message that the group’s militiamen have mobilized and been put on high alert.

Jawad al-Talibawi, a spokesman for the armed wing of Asaib Ahl al-Haq, another Iranian-aligned militia, said the group had mobilized 1,500 members of its special forces to enter Anbar.

“Those 1,500 fighters are now awaiting the order to go in,” Talibawi said by telephone.

Omar al-Alwani, a pro-government tribal fighter from Ramadi, said no soldiers are left to defend eastern roads to Baghdad. He said he was among those who fled Malaab with the group of pro-government forces, which he estimated at more than 500. They left behind weapons that included artillery, machine-gun trucks and machine guns, he said.

“Daesh seized the police station, the big mosque” in the area, he said, adding that Islamic State fighters surrounded the area police station and fatally shot the senior officer there, Col. Muthana al-Jabari.

He and others expressed concern about several hundred pro-government forces who were still surrounded by militants in a military operations hub in the city. According to unconfirmed reports, as many as 40 people in that facility were killed Sunday in two suicide bombings.

“Only God can help those people now. There is no one left to protect them,” said Alwani, the tribal fighter.

But Majed Abdullah, a captain in the Iraqi army who was among those besieged in the compound, said that scores of pro-government forces managed to escape the facility. They drove west, he said, adding that they left behind dozens of wounded soldiers and police officers. It was unclear whether the Islamic State had entered the compound.

“We’re on the Iraq-Jordan highway now, and we’re waiting for orders to either reconstitute our forces and attack or retreat entirely,” Abdullah said by telephone.

The militants did not appear to be attempting attacks on Baghdad, a maneuver that the group’s commanders probably realize would involve facing formidable resistance from the significant layers of defense, including Shiite militias, protecting the capital.

Using car bombings and heavy shelling, Islamic State militants launched a surprise attack Thursday on Ramadi, capturing most of the city’s neighborhoods by the next day. Residents, security forces and officials accuse the militants of carrying out executions and systematically destroying homes belonging to members of the security services.

Before the assault Thursday, the Islamic State had already taken control of most of Anbar during sweeping advances last summer throughout Iraq.

A decade ago, U.S. forces sustained heavy casualties trying to put down an insurgency in Anbar that was led by the group al-Qaeda in Iraq, the precursor to the Islamic State. But Sunni tribal figures in the province, with U.S. backing, turned on the terrorist group, driving it from Anbar and helping to bring the province back under the control of Baghdad.

Only a week ago, officials in Anbar were touting a new plan to form a force of tribal fighters to battle the Islamic State in the province. But with the extremist group’s capture of Ramadi, the plan has been all but derailed.

Rafia al-Fahdawi, an elder in the province’s Albu Fahed tribe, expressed doubt that a similar tribal uprising could be waged at the moment against the extremist group. On Saturday, he and dozens of fellow Sunni tribal leaders also issued a call for Shiite militias to intervene in Anbar.

“The army has let us down. The SWAT team has let us down. We can’t depend on these forces, and we need forces that are inspired to fight hard,” he said, referring to the militias.

Read more:

Iraqi Sunnis flee Anbar only to find new dangers in Baghdad

The Islamic State is failing at being a state

Islamic State appears to be fraying from within

Today’s coverage from Post correspondents around the world