On the other side of the walls, shops lie shuttered; alleys are blanketed by silence. Padlocked red doors, built into the partition, prevent Shiite visitors from mixing with the city's mostly Sunni citizens. Here, Mohammed al-Saeed, a Sunni shopkeeper, fumes.

"This wall is a sectarian wall," he said. "They don't trust us."

The destruction of the venerated mosque in this central Iraqi city in 2006 has come to be seen as the spark for the terrible sectarian violence that gripped Iraq. Now, the Iraqi government holds up Samarra as evidence that peace is possible, even in the country's most contentious areas. But the quiet here is a brittle one, where Shiites exercise dominance and alienated Sunnis wallow in resentment.

"These walls give an idea like death is waiting for us," declared Mohammed Hussen, a local Sunni council leader. "Their ambition is to make Samarra into a Shiite city."

As Iraq marks the sixth anniversary of the fall of Saddam Hussein this month, attacks on Shiite areas in Baghdad have highlighted the enduring tensions between the nation's two dominant sects. In cities such as Samarra, fresh struggles are underway to control areas and consolidate power and resources ahead of the withdrawal of U.S. troops, scheduled for this summer. These contests pit local forces against the central government -- a reminder of how Iraq remains a patchwork of tribes more loyal to sect, ethnicity and region than a national identity at a time when Iraq, tired of war, needs unity the most.

"The people really can't stand us," said Osama Hussein Ali, 20, a Shiite national policeman from Baghdad who works near the shrine. "Whatever we do for the city, they reject it. It seems they want to go back to the previous situation."

"They hate checkpoints. They hate order."

American military commanders say Iraq's security forces have made progress in combating sectarianism within their ranks. But they are still concerned that many policemen and soldiers remain riven by sect and ethnicity, raising the possibility of infighting and instability after U.S. combat troops leave.

"They are not where any of us want them to be," said Maj. Gen David G. Perkins, the U.S. military's top spokesman in Iraq.

Three years ago, a series of bombs, placed in various corners of the shrine, shattered the gold dome of the 10th-century Askari mosque, which houses the remains of two prominent Shiite imams. The U.S. military and the Iraqi government virtually shut down the city as cycles of brutality between Sunnis and Shiites pushed the nation toward the brink of civil war. Outsiders, the vast majority of them Shiites, were brought in to rebuild the shrine.

Today, the city of oatmeal-colored minarets that straddles the Tigris River feels like a military base, with streets tangled by blast walls and checkpoints.

Backed by U.S. troops and advisers, Iraq's mostly Shiite national police and army control the city. They coexist uneasily with the local Sunni police force and the Sons of Iraq -- former Sunni insurgents who turned against the militant group al-Qaeda in Iraq and allied with the U.S. military.

Neither the local police nor the Sons of Iraq are allowed to protect the shrine, which is guarded by an array of mostly Shiite units sent by the central government.

"I don't believe that any people or city feel comfortable when they have an army from outside. The traditions from their areas are different than ours," said Sheik Mudher al-Naisani, a Sunni tribal leader. "That's right, this is one country. But it is better for Iraq that each serve in their own areas."

While most Iraqis believe that al-Qaeda in Iraq insurgents planted the bombs, many Sunni leaders here place the blame on the national police and U.S. troops who were guarding the shrine. Members of Iraq's national police force have committed some of the most horrendous sectarian crimes since the 2003 U.S.-led invasion; to this day there are widespread suspicions of infiltration by Shiite militias.

"It was a conspiracy," said Hussen, the Sunni council leader.

On a recent morning, former Iranian president Ali Akbar Hashemi Rafsanjani arrived at the shrine from Baghdad, 78 miles away. Shiite and Kurdish soldiers, dispatched by the central government, protected him.

For many Sunni residents, it was the latest sign of the growing influence of Iran's Shiite theocracy over Iraq's government -- and of the degree to which Shiites dominate the city.

"It is an insult. They are the reason for the ruin of this city," a Sunni shopkeeper said. As he spoke, Shiite and Kurdish soldiers ordered people to move away from the entrance to the shrine.

"Who do they think they are? I am in my own country," the shopkeeper said before fading into a narrow, lonesome alley flanked by the walls.

On the other side, Rafsanjani walked along the wall, followed by his entourage. They stepped into the shrine's large courtyard, circled by walls covered with ornate yellow and blue tiles. Today, the nooks where the bombs were placed are covered with glass panes -- not least because an investigation is still ongoing. A large yellow crane hovers above the dome, now a hull.

A few feet away, Gen. Rashid Flayeh, Samarra's Shiite military commander, said he had fired 385 national policemen in the past 18 months for "having sectarian feelings." Now, he said, 500 local Sunnis have joined the national police. He promised that, eventually, authority would be handed to the local police. But Flayeh acknowledged that sectarian tensions persist. He accused some Sunni leaders of wanting American forces to remain in the city so that they could benefit from U.S. funds for providing intelligence tips.

"Only a few people are trying to raise sectarian tensions between Sunnis and Shiites," Flayeh said.

Not far from the shrine, Sons of Iraq leaders and local councilmen sat in a small room at their headquarters guarded by local policemen.

They said they had expected Samarra residents to have a greater role in the city's resurrection. Only 30 Sunnis from Samarra have been hired to rebuild the mosque, shrine officials said. Many Sunnis had also expected to profit from the reopening: Around the holy shrines in the southern cities of Najaf and Karbala, shopkeepers thrive on the influx of thousands of pilgrims. But the walls have suffocated Samarra's local economy. "It's frustrating. We're the ones who kicked out al-Qaeda," said Omar Muhammed Hassan, the head of Samarra's local council.

Inevitably, the conversation turned to the "outsiders" who have infiltrated the city.

"Most of the Samarra people hate the national police," said Col. Suhail Latouf Fadhil, a former insurgent and officer in Saddam Hussein's army. "The trouble we face with the national police is more than we face with al-Qaeda."

Outside the headquarters, Haider Fallah, 22, a local policeman, said he had been stopped at national police checkpoints for no reason and searched -- even after he flashed his police identification card.

"They think all people of Samarra are terrorists," said Arkan Majid, 29, a local policeman standing beside Fallah.

"They believe that only they have the right to protect the shrine -- not us," said Ahmed Yahya Yaseen, 28, another local police officer.

A few blocks way, two national policemen from the southern Shiite city of Kut said the local police and the Sons of Iraq movement had been infiltrated by insurgents.

"We don't trust them," said Taher Kazal, 29.

Two weeks ago, a Shiite national police officer had approached a young woman, a relative of a local Sunni police officer. A fight broke out between the men, and "some people used this incident to provoke sectarianism," Flayeh, the Shiite commander, said, smiling. "But now they are friends."

The Shiite officer he was referring to stood next to him at the shrine. He, too, smiled.

In the Sons of Iraq headquarters, another version emerged: The Shiite policeman had tried to make advances on the wife of the local Sunni officer. The Shiite man, local Sunni leaders were told, had been suspended from the police force, pending an investigation.

At that moment, Misr Flayer Hassan, the Sunni deputy head of the local council, decided to inquire about the progress of the case. He called a national police officer, who told Hassan that they had not seen the Shiite man since the incident.

"We are very patient, but it will not last forever," Hassan said.