BAGHDAD—Iraqi special forces advanced to the edge of Fallujah on Monday but struggled to enter the city, where Iraqi and U.S. officials said Islamic State extremists were amassing civilians to serve as human shields.
The offensive against Fallujah, Islamic State’s second-biggest urban stronghold in Iraq after Mosul, aims to dislodge the Sunni extremists from the Iraqi city they have occupied the longest.
If successful, it could significantly weaken them ahead of an advance on much-larger Mosul, long planned by the government and the U.S.-led coalition supporting its fight against Islamic State.
The Fallujah operation, led so far by Shiite militias and army and police forces, has almost completely cleared the city’s perimeter of Islamic State fighters since it was launched a week ago. But the next, crucial stage of that operation, led by Iraq’s U.S.-trained counterterrorism forces, got off to a fitful start Monday.
“We are at the entrance of the city, but not inside yet,” Lt. Gen. Abdelwahab al-Saadi, commander of the Fallujah operation, said by telephone. “They are resisting.”
“We assess that the forces are near the city limits,” said Col. Steve Warren, spokesman for the U.S.-led coalition in the fight against Islamic State.
Fallujah is an almost exclusively Sunni city in the desert province of Anbar—the vast heartland of Iraq’s Sunni minority—and the battle to retake it is particularly significant for Iraq’s fight against Islamic State.
More than a decade ago, Fallujah was a base for al Qaeda in Iraq, the insurgent group that developed into Islamic State. Islamic State faced little resistance when it swept into the city in January 2014, even before it stormed the country’s north and took the city of Mosul, laying claim to a so-called caliphate across Iraq and Syria.
© KHALID MOHAMMED/ASSOCIATED PRESSWinning Fallujah could boost Prime Minister Haider al-Abadi, who has faced political upheaval in recent months as street protesters demanded changes that lawmakers are too deadlocked to make.
However, the Fallujah operation carries many risks and unknowns, Iraqi and U.S. officials said. One is the overtly sectarian tone of the battle, as Shiite militias deeply resented by many Sunnis took a lead in the early stage of the offensive around the city and Iran dispatched advisers to the battlefield, according to militia fighters and leaders.
Under an agreement with the government, the Shiite militias are supposed to stay out of the fight in the city itself. But their involvement in the battle so far has enraged Iraqi Sunnis and frightened Fallujah residents, who fear the Shiites will carry out revenge killings.
Ibrahim al-Jumaili, a Fallujah native who fled three months ago, said his family and friends in the city see “death at the door,” but many are frozen in fear.
“They do not believe they can survive, because different sides want to kill them—Daesh, Shiite militias, or security forces,” Mr. Jumaili said, using an Arabic acronym for Islamic State and reflecting distrust among many Fallujah residents of the Shiite-dominated army.
Sunnis regionwide, from Saudi Arabia to Lebanon, have reacted with outrage to the unfolding battle in Iraq, which many have come to see as a sectarian face-off, even as Iraqi Shiite leaders have called on their forces to protect civilians and show discipline.
The U.S. backs Iraqi forces in the Fallujah operation with airstrikes, but has expressed concern about the role there of the Shiite militias. Anticipating a tough battle in Fallujah, American officials advised their Iraqi counterparts not to head for Fallujah and to instead focus on preparing for the Mosul battle.
As the urban offensive took off, the more immediate threat to Fallujah’s civilians came from Islamic State, which was forcibly gathering many civilians into the city center, Iraqi and U.S. officials said. They described the move as possibly intended to ward off U.S.-led coalition airstrikes on the city, which have been hitting militant targets for months.
At least 50,000 civilians are believed to be trapped in Fallujah, suffering under harsh living conditions after a nearly yearlong siege by the army and militia forces. About 5,000 people have made it out in the past week in a complicated evacuation process, according to humanitarian aid workers.
“Since the start of the Fallujah operation a week ago, Daesh is forcing people to the center of Fallujah, threatening to kill people if they do not listen,” said Fallujah’s mayor, Eissa al-Issawi.
Coalition spokesman Col. Warren said the extremists used the same tactic in the battle for Ramadi, the capital of Anbar province, which Iraqi forces backed by coalition airstrikes retook in December after seven months of battle. “It does complicate efforts to get people out,” Mr. Warren said.
The combined risks Fallujah’s remaining population confronts are among the worst civilians have encountered in the anti-Islamic State battle so far, Iraqi officials and humanitarian aid workers said.
Lise Grande, the United Nations’ top humanitarian official in Iraq, said the U.N. was concerned about “artillery and crossfire, the lack of food, and the reported herding of civilians into the city center.” Ms. Grande also said the city could also be “days away from a cholera outbreak” as clean water dwindles.
Aid officials say there are no safe routes out of Fallujah, and that many left there are too afraid—or too resigned—to risk trying to leave. In the city, militants hunt down people rumored to be planning an escape in their homes and on the streets, fleeing residents say. Mr. Issawi, the mayor, said a clash broke out Monday between a group trying to flee and Islamic State fighters.
Estimates by Iraqi and American officials on the number of militants in the city vary from 500 to 2,000, making it difficult to predict the battle’s course. In 2004, when Fallujah was a stronghold for al Qaeda in Iraq, U.S. Marines led two separate battles there in the costliest operations of the Iraq war—and some of the bloodiest for American forces since the Vietnam War.
The start of the push into Fallujah on Monday came as three bombings killed 22 people in the capital Baghdad. One of them, in which a parked motorcycle blew up, killing three people, occurred in Sadr City, a Shiite-majority neighborhood where Islamic State claimed responsibility for a series of bombings earlier this month, bringing terror and tight security back to the capital.