Red and green Shiite banners line the streets of Baghdad, portraits of religious figures and slain "martyrs" stare down from billboards, hymns blare from shops and cafes, and grim-faced militiamen prowl the streets in pickup trucks.

The holy month of Muharram has brought an unprecedented show of strength by Iraq's Shiite Muslim majority, underscoring its domination of the bitterly fractured capital and the vulnerability of the once-dominant Sunnis, while raising fears of a new round of sectarian cleansing by Shiite militias allied with the government.

"They want to turn Baghdad into a purely Shiite city," said Abu Abdullah, a community leader in Baghdad's Sunni enclave of Azamiyah, who asked that his full name not be published for fear of retribution.

Muharram — a period of mourning over the death of Imam Hussein in a 7th century battle that cemented Islam's Sunni-Shiite divide — is observed with grieving and fasting by Shiites across the region.

But this year in Iraq the traditional Muharram banners are being unfurled at a time when large numbers of Shiite militiamen are battling alongside the army against the Sunni extremists of the Islamic State group, which has seized a third of the county and massacred hundreds of Shiites, whom it views as apostates.

Religious banners and portraits of Imam Hussein hang from homes, bridges, stores and even colleges across much of Baghdad and can be seen even in Sunni-majority areas. They also adorn government buildings and hundreds of security checkpoints across the city, reinforcing Sunni fears that Shiite Prime Minister Haider al-Abadi is no less sectarian than his predecessor, Nouri al-Maliki, whose policies were widely seen as aggravating Sunni grievances.

Sunnis say Shiite militiamen drive through their streets in pickup trucks, brandishing weapons and blaring Muharram hymns. Some Sunnis say they themselves hang Shiite religious banners from their homes to avoid unwanted attention.

Shiites reject the accusations, saying they should be free to openly practice their religion after decades of marginalization and abuse under successive Sunni-led dictatorships.

"The Sunnis have ruled for 1,400 years, it's our time now. What do they want? They want us to be the slaves and they the masters?" said Hashem Enad, a 50-year-old father of 10 who runs a photography studio in the sprawling Shiite district of Sadr City. "We don't force anyone to fly Shiite banners," he said.

"Who is fighting the Islamic State? We are," said Mohammed Hanash Abbas, a Shiite and co-owner of a bookshop in a part of the old city dating back to the Ottoman era. "And how many Sunnis have volunteered to fight Daesh? Very few," he said, using the Arabic acronym for the group.

Other Shiites go further, pointing to the city's persistent bombing attacks as evidence of sleeper cells among their Sunni neighbors.

The other bookshop owner, Shiite Atallah Zeidan, acknowledged that Sunnis live in "genuine fear" of Shiite militias, but said the divide is political and not religious. "All this sectarianism is created by politics. It is about power. Ordinary folks will get along just fine if left alone."

Iraq's long-dominant Sunni minority saw its power rapidly erode following the 2003 U.S.-led invasion that toppled Sunni dictator Saddam Hussein and brought Shiite religious parties — many with strong ties to Shiite Iran — to power.

Sunni grievances against the Shiite-led government were a key factor in the Islamic State's lightning offensive over the summer, which in turn prompted the remobilization of Shiite militias and an influx of Iranian military advisers, raising fears of a return to the sectarian violence that convulsed the country in 2006 and 2007.

The carnage of those years redrew the map of Baghdad, a once-cosmopolitan city where Sunnis, Shiites, Christians and Kurds lived side-by-side for centuries, with the Sunnis the dominant class. The violence emptied out the capital's most diverse neighborhoods and left it with a Shiite majority estimated at 70-80 percent, with hundreds of thousands of Sunnis fleeing the city and the holdouts squeezed into scattered enclaves.

Today, billboards feature Shiite "martyrs" who fell in battle against the Islamic State group alongside the late Iranian leader Ayatollah Ruhollah Khomeini and his successor Ayatollah Ali Khamenei — a remarkable sight in a country that fought a devastating eight-year war with Iran in the 1980s.

A senior official at the government's internal security agency, who spoke on condition of anonymity because he was not authorized to talk to reporters, acknowledged that some Shiite militiamen were using their membership in the "popular mobilization" forces as a cover to intimidate Baghdad's Sunnis.

Dozens of people were killed last summer in sectarian attacks, but the violence eventually died down and there has been no sign of a return to the mass violence of eight years ago, when dozens of people were abducted, tortured and killed on a daily basis. And yet concrete barriers erected around the city's most volatile neighborhoods a decade ago remain in place.

Baghdad's Sunnis and Shiites alike are terrified of the Islamic State group, which has imposed a harsh version of Islamic law, or Sharia, in areas it controls in Syria and Iraq and massacred those standing in its way, including fellow Sunnis.

Earlier this month the group killed scores of male members of a prominent Sunni tribe in the western Anbar province, offering a chilling glimpse of what could await both Shiites and many Sunnis if the capital were to fall.

Iraq's media has strived to portray the country as united against a common threat, repeatedly showing footage of Sunni clerics and tribesmen rallying against the Islamic State or calling on Iraqis to close ranks against it.

But Khalil Abu Omar, a 46-year-old resident of Baghdad's mainly Sunni Mansour district, said the icy rapprochement between the capital's Shiites and Sunnis is "a question of mutual interests, not a common understanding."

"It is temporary," added the father of four, who sent his teenage son to Turkey, fearing that his age and sect would make him a kidnapping target.