Snaking past blackened shop fronts and shattered homes, buses ferried the first civilian residents back to Tikrit this week, an initial step toward reviving this city after Islamic State militants were expelled more than two months ago.

Children pressed their faces to the bus windows as the 200 families returned. Police and militiamen in the city fired bursts of bullets into the air in celebration.

The entire population of Tikrit, around 150,000 people, had been forced outbythe war, joining around 3 million Iraqis displaced by fighting across the country. Returning people to their homes as territory is won back from Islamic State militants is a huge challenge for the Iraqi government, and one fraught with sensitivities.

Whether the state succeeds could determine whether the country can recover its unity after a war that has divided the country.

In trying to resettle residents, the government faces difficulties ranging from tribal feuding to security concerns to restoring services. Perhaps most significantly, returning Sunni residents are viewed with suspicion by Shiite militia groups who have driven out the Islamic State, raising fears of sectarian bloodletting.

"It's very sad to see wide areas empty, towns empty, villages empty, farms empty," said Hisham al-Suhail, head of the Iraqi parliament's reconciliation committee. "Now we are moving in the right direction."

The battle for Salahuddin province and its capital Tikrit earlier this year marked the government's biggest victory against Islamic State militants, and the first time it retook a major population center.

Those returning to Tikrit this week came back to a city nearly devoid of services. Its main hospital is destroyed, and water and power are yet to be fully restored. The city was ravaged by fighting, and then suffered looting by Shiite militiamen. There is still a risk of unexploded ordnance, and ambulances were parked on standby on the city's streets Monday as the first buses arrived.

"We've told families not to all go into their homes at the same time, just one at a time," in case there are explosives, said Ahmed al-Karim, the head of the governing council for Salahuddin province.

A major worry is the role that will be played by Shiite militias that helped expel the Islamic State from the city. Some Shiite fighters have suspected that Sunni residents supported the Islamic State, which proclaimed itself champion of the Sunnis.

"It's a big concern to us with the return of the families. We are concerned about acts of revenge, especially in Tikrit, because of the Speicher massacre," said Raed al-Jabbouri, the governor of Salahuddin province. He was referring to the brutal execution of an estimated 1,700 soldiers in the city by the Islamic State. Pictures of the massacre — taken from video that the Islamic State released — have been hung on the city's main streets.

The city's liberation was followed by widespread looting, and some 400 houses were destroyed, said Jabbouri.

Lines of shops, which were unscathed on the day after the city was retaken by pro-government forces, are now scorched.

However, Shiite militiamen appeared to have largely withdrawn by the time families returned, in accordance with a government order. Local police forces and militiamen from the city itself are keeping order.

Asil Hamid, 23, who returned with her husband and her three children, found her parents' house blackened by fire. A family friend in the local police force said it had been in good shape when he had checked it 10 days earlier. She broke down as she left the acrid-smelling building.

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Meanwhile, in the countryside of Salahuddin province, the return of civilians to some areas has been complicated by tribal feuding.

"It's not just Sunni, Shia, Kurd, as people like to think. It's Sunni on Sunni, tribe on tribe — such a kaleidoscope," said a U.S. official, speaking on the condition of anonymity because of the sensitivity of the subject.

Sunni and Shiite tribes that fought alongside the government have objected to the return of members of other tribes who sided with the Islamic State before the ouster of the extremists.

On the outskirts of Tikrit, village after village lies deserted, aside from occasional militia outposts. Bombed-out garages and restaurants mark the landscape.

In Alam, around six miles northeast of Tikrit, families have been allowed to return since the village was cleared of militants in March. The Sunni tribe there had fought alongside the government forces. But the nearby villages of Dawr and Abu Ajeel, where many villagers supported the Islamic State, remain empty.

After months of negotiations between the tribes, there is now an agreement that families from those two villages who did not cooperate with the Islamic State should be allowed to return — but emotions run high.

The bodies of 13 Alam residents publicly executed by the Islamic State were found in Abu Ajeel after it was retaken from militants.

"There is a lot of tension and we receive many, many demands, especially from the young people, not to allow them [local residents] to return because they've killed so many people," said Marwan al-Jabbara, head of Salahuddin's tribal council. "But we can't just banish a whole tribe. We have to return the innocents."

Now, the nearest populated area to Alam that is not occupied by Islamic State is the city of Samarra, some 35 miles away. There are vast stretches of territory in between that have been liberated, but are empty. "It's lonely here," Jabbara said.

In Yathrab, a lush agricultural area of vineyards and sunflower fields further south, negotiations have been particularly knotty. Here, the dominant tribe is comprised of both Shiites and Sunnis. The Shiite members had demanded "blood money" from the Sunni side in order for families to return. Around 60,000 largely Sunni families are still displaced from the town.

"It's tribal law, tradition," said Yousif Mohammed Al Tamimi, who is negotiating for the Shiite faction of the tribe. "If members of any tribe kill someone from another, they should pay money or there will be retribution."

The government has stepped in and agreed to pay blood money of around $20,000 for each victim, Tamimi and other officials said. But with similar payments needed to settle disputes across the country, the financial burden is huge, said Suhail, the member of parliament.

"The problem increases every time we liberate an area," he said. "The terrorists are destroying and destroying, and we have to mend our communities."

Those who have "blood on their hands" or cooperated with Islamic State militants will never be allowed back, he said.

But even with tribal leaders moving toward reconciliation, many ordinary people say they are not close to forgiving. As part of the Yathrab negotiations, the hamlet of Fadous is claiming blood money for 18 villagers killed in a September attack.

Even if reparations are paid, they say, they want a buffer zone between the Shiite branch of the tribe and the Sunni side, who they accuse of siding with the Islamic State.

Zaina Fares Aswad said she lost eight members of her extended family in that attack, including her 17-year-old son.

If the Sunni tribal members return, "I'll behead them myself," she said.