The al-Askari shrine in the Iraqi city of Samarra is surrounded by thousands of Shiite militiamen in mismatched uniforms, many of them awaiting transport to the nearby front lines of the war against the Islamic State group.

For months, they have fended off attacks by the extremists and now they are on the offensive in Tikrit to the north, but their presence has alarmed Samarra's mainly Sunni residents, who fear both sides of the increasingly sectarian conflict.

The golden-domed shrine is among the holiest sites in Shiite Islam, and pilgrims from neighboring Iran continue to flock there despite the fighting. In 2006, Sunni extremists bombed the site, sparking a wave of sectarian bloodletting across the country that killed tens of thousands of people.

As the Islamic State group swept across Iraq last summer, Shiite militiamen heeding a call from the country's top cleric flooded into Samarra to defend the shrine and halted the militants' advance 60 miles (95 kilometers) north of Baghdad. Today, the area around the shrine is festooned with militia banners and portraits of Iraqi and Iranian Shiite clerics.

But just across the city there is a conspicuous lack of security forces, and while traffic flows and shops are open during the day, residents say they are walking on eggshells.

"We're concerned about the presence of the militias, with regard to kidnappings and killings," said Ghani Younis Hassan, the owner of a children's clothing shop, who said he doesn't let his wife and children walk the streets for fear of harassment.

"They feel that the shrine justifies their presence here," he added. "It's the militias who have the power, not the military, so we feel a lot of concern and unease."

The United States spent billions of dollars training and equipping Iraq's army during its eight-year occupation, only to see security forces crumble last summer when the Islamic State group rampaged across the north, capturing the country's second-largest city Mosul as well as Tikrit, Saddam Hussein's hometown.

The rapidly mobilized Shiite militias halted the Islamic State advance and have successfully defended Samarra, which is home to a famed ninth century A.D. spiral minaret and is considered a UNESCO world heritage site. The structure is still standing, but today it is covered in black and red graffiti hailing the various militias.

Human rights groups say Shiite militiamen in other parts of Iraq have carried out revenge attacks against Sunni civilians. The reported kidnappings and killings pale in comparison to the well-publicized atrocities committed by the Islamic State group, but have complicated efforts to mend the war-ravaged country's sectarian divide.

Iraqi officials believe Samarra — the last major city between Baghdad and the Islamic State's self-styled caliphate — is still vulnerable, despite the heavy security presence. Even more Shiite militiamen have streamed in since the launch of the Tikrit offensive earlier this month, with many setting up bases in the city.

The city is also hosting Sunnis who fled the Islamic State group or were displaced by the fighting.

At a half-built school now housing residents from the nearby village of Kashiefa, one displaced Sunni man, who spoke on condition of anonymity for fear of retribution, said the militias visit the camp on occasion, confiscating what few belongings the displaced have, including government food aid.

Majda Hamoudi, a displaced woman, said neighbors had called to tell her that Shiite militiamen destroyed her home.

"We were afraid of Daesh and now we are afraid of the militias. It doesn't end for us," she said, using an Arabic acronym for the Islamic State group.

The Shiite militiamen deny such accusations, and say they distrust the Sunni residents of the city they are defending.

"Daesh consists of 10 percent foreigners and 90 percent residents of the area," said Sheikh Jaber al-Lami, a militia fighter from Baghdad. "We're the ones who are defending this city — it's (the Sunnis) who let them come into this area in the first place."

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