MUQDADIYA, IRAQ — The room seethed with anger as Sunni Arab members of a neighborhood guard force brought in a freed captive, who stood mute amid the raised voices and swirling cigarette smoke.
Eyeing a visiting U.S. Army officer, the burly gunmen in camouflage coaxed the man to raise his arms and display the brown shoelaces that bound his wrists. The man, a fuel vendor, said he had been stopped by Shiite guards who demanded to know his sect. When he told them he was Sunni, he said, "they tied my hands, they slapped and kicked me. They stole fuel from me too."
He was released, he said, when he told his captors that his relatives were Shiite.
Both the Sunni and Shiite guards are helping the U.S. military defend Muqdadiya's Matar district from Sunni extremists who forced the city into a self-styled Islamic caliphate for more than a year. But though the two groups run checkpoints around the corner from each other, each takes every opportunity to convince the Americans that the other is not to be trusted.
The rivalry illustrates the difficulties the U.S. military faces as it tries to duplicate in religiously mixed regions of Iraq a strategy that produced a dramatic turnaround in Anbar, an overwhelmingly Sunni province.
U.S. commanders and residents agree that the fighters, once dubbed concerned local citizens by the Americans, and now known as Sons of Iraq, have played a key role in forcing the group Al Qaeda in Iraq and affiliated Sunni insurgents out of Muqdadiya, about 60 miles northeast of Baghdad. But as the militant organizations have retreated, rival bands of Sunni and Shiite guards have raced to stake claims to the vacated areas, raising the specter of sectarian bloodshed.
Lt. Col. Mark Landes, commander of the 2nd Battalion, 23rd Infantry Regiment, in Muqdadiya, called the rivalry "a huge concern." Landes' hope is that by working on the same side, they will find a way to overcome their differences. But there is little sign of that yet. The U.S.-allied Sunni fighters who gathered in a tiny office at a hospital-turned-security base in Matar were blunt about relations with their Shiite counterparts.
"In this country, there are two enemies," said one of the Sunni leaders, a giant of a man in a bulletproof vest who gave his name only as Abdulrahman. "Now we are fighting Al Qaeda, but in the future we must deal with another enemy, the Mahdi Army."
Abdulrahman accuses the Shiite guards of belonging to that militia, a group affiliated with radical cleric Muqtada Sadr that he says terrorizes Sunni civilians such as the fuel vendor. Shiite fighters counter that Abdulrahman's men have been infiltrated by Al Qaeda in Iraq extremists.
U.S. officers warn that the reluctance of the heavily Shiite police hierarchy to incorporate Sunni members into their ranks could one day spur the Sunnis to turn their guns against the Shiite-led government.
The government embraced the Sunni tribesmen, whose unexpected rebellion last year helped drive Al Qaeda in Iraq out of large parts of Anbar, west of Baghdad. Thousands of them now fill the ranks of the province's depleted security forces.
But the Iraqi government has resisted U.S. attempts to recruit Sunni allies in Baghdad, Diyala and other areas that include large numbers of Shiites, because it fears the Shiites could become targets once U.S. forces are no longer there.
Iraq's defense and interior ministers have made it clear that the volunteers would have to join the police and army or find alternative employment. But they said there was room in the official security forces for only about 20% of the more than 80,000 volunteers working with the Americans in central and northern Iraq.
In Muqdadiya, a city of about 200,000, the U.S. military is paying more than 1,000 volunteers about $10 a day to help police their neighborhoods.
The city's Sunni mayor, Najim Harbie, is a strong proponent of the program. But he says the central government has agreed to hire only 120 of the volunteers, who include roughly equal numbers of Shiites and Sunnis.
U.S. officials, who say they respect the government's wishes and cannot continue paying the volunteers indefinitely, are proposing training to help the rest find civilian jobs.
But Harbie said, "In Iraq right now, there are no jobs apart from the police and army." If the Americans stop paying the volunteers, he said, "it will be back to square one."
Muqdadiya, an ethnically and religiously mixed city on the edge of the verdant Diyala River valley, has suffered successive rounds of sectarian fighting among Shiite and Sunni militants since the U.S.-led invasion of Iraq in 2003.
By mid-2006, it was essentially under the control of Sunni insurgents. U.S. troops, whose priority was to secure Baghdad and the Diyala provincial capital, Baqubah, did not attempt to reclaim Muqdadiya until a year later.