Nearly four dozen Sunni detainees were gunned down at a jail north of Baghdad, a car bomb struck a Shia neighbourhood of the capital and four young Sunnis were found slain, as ominous signs emerged Tuesday that open warfare between the two main Muslim sects has returned to Iraq.

The killings, following the capture by Sunni insurgents of a large swath of the country stretching to Syria, were the first hints of the beginnings of a return to sectarian bloodletting that nearly tore the country apart in 2006 and 2007.

During the United States' eight-year presence in Iraq, American forces acted as a buffer between the two Islamic sects, albeit with limited success. The U.S. military is now being pulled back in — with a far more limited mission and far fewer troops, as President Barack Obama nears a decision on an array of options for combating the Islamic militants.

In the latest sect-on-sect violence, at least 44 Sunni detainees were slaughtered by gun shots to the head and chest by pro-government Shia militiamen after Sunni insurgents tried to storm the jail near Baqouba, northeast of Baghdad, police said.

The Iraqi military gave a different account and put the death toll at 52, insisting the Sunni inmates were killed by mortar shells in the attack late Monday on the facility.

In Baghdad, the bullet-riddled bodies of four men in their late 20s or early 30s, presumably Sunnis, were found Tuesday at different locations in the Shia neighbourhood of Benouk, according to police and morgue officials who spoke on condition of anonymity because they were not authorized to talk with the media.

Also Tuesday, a car bomb in Baghdad's Shiite Sadr City district killed 12 people and wounded 30 in a crowded outdoor market, police and hospital officials said. No one claimed responsibility for the bombing, but attacks targeting Shia districts are routinely the work of Sunni militants.

The sectarian violence was a grim reminder of a dark chapter in Iraq's history when nearly a decade ago the city woke up virtually every morning to find dozens of bodies dumped in the streets, trash heaps or in the Tigris river, bullet-riddled or with torture marks.

And with the al-Qaeda breakaway group the Islamic State of Iraq and Syria (ISIS) continuing its lightning advance toward Baghdad, there are fears the situation could get worse.

CBC correspondent Nahlah Ayed, reporting Tuesday from the city of Erbil in northern Iraq, said that fighting so close to Baghdad is making people in the capital nervous, and similar concerns are evident in Erbil, which is less than 100 kilometres from the fallen city of Mosul.

"We saw huge lineups of people going to gas stations, filling up in case they have to escape," she said.

Kurdish Peshmerga battle ISIS

Ayed was in Erbil to speak with Kurdish Peshmerga fighters who have been taking on ISIS.

Col. Hazhar Ismail

Col. Hazhar Ismail, a peshmerga spokesman, said Iraq's government has itself to blame for the growing insurgency in the country. (CBC)

Serwan Karim, 34, who was recovering at a local hospital after being shot during a firefight with ISIS, said the peshmerga are the only army strong and capable enough to take on the militants.

"Tomorrow if I'm better I'll go back to fight," he said.

Col. Hazhar Ismail, a peshmerga spokesman, warned Iraq’s government is facing a wider threat than the one posed by ISIS. 

"It looks like revolution against the Iraqi side," he said, adding that Nouri al-Maliki’s government has itself to blame.

Ismail said Iraq’s government had the chance to reach out to Sunnis and other minority groups but chose not to.

"So now they have to look for the solutions for the problems they created," he said.

"The problem, there’s no trust.  That’s the biggest problem in Iraq."

Conflicting details

There were conflicting details about the clashes in the al-Kattoun district near Baqouba, the capital of Diyala province and one of the bloodiest battlefields of the U.S.-led war, and on how the detainees were killed. The city is 60 kilometres northeast of the Iraqi capital.

IRAQ-SECURITY/

Personnel from the Kurdish security forces detain a man suspected of being a militant belonging to the al Qaeda-linked Islamic State in Iraq and Syria in the outskirts of Kirkuk. Iraq is in danger of sliding back to the wholesale Shia-Sunni bloodletting of 2006 and 2007. (Ako Rasheed/Reuters)

Officers said the local police station, which has a small jail, came under attack Monday night by Sunni militants who arrived in two sedan cars to free the detainees. The militants fired rocket-propelled grenades on the building before opening fire with assault rifles.

A SWAT team accompanied by Shia militiamen rushed to scene and asked the local policemen to leave, according to the officers. When the police later returned to the station, they found all those in the detention cells dead.

The bodies were taken to the Baqouba morgue, where an official said most had gunshot wounds to the head and chest. One detainee, however, survived and was taken to the hospital.

Police later arrived at the hospital and took the wounded man away, said a hospital official.
 
The police officers, the hospital and morgue officials all spoke on condition of anonymity, fearing for their own safety.
 
A different account was provided to The Associated Press by Iraq's chief military spokesman, Lt.-Gen. Qassim al-Moussawi. He said 52 detainees who were held at the station in al-Kattoun died when the attackers from the Islamic State shelled it with mortars. 
 
Nine of the attackers were killed, al-Moussawi said.

ISIS vows to march on Baghdad

The Islamic State is known to be active in Diyala, a volatile province with a mix of Sunnis, Shias and Kurds and where Shia militiamen are deployed alongside government forces. Sunni militants have for years targeted security forces and Shia civilians in the province, which abuts the Iranian border.

The Islamic State has vowed to march to Baghdad, and the Shia holy cities of Karbala and Najaf in the worst threat to Iraq's stability since U.S. troops left. The three cities are home to some of the most revered Shia shrines. The Islamic State has also tried to capture the city of Samarra north of Baghdad, home to another major Shia shrine.

CBC correspondent Sasa Petricic, reporting from a checkpoint between Mosul and Erbil, said some of those fleeing Mosul are Sunni.

IRAQ-SECURITY

Members of the Kurdish security forces man a checkpoint in the outskirts of Kirkuk. CBC's Sasa Petricic said from a checkpoint between Mosul and Erbil that he spoke to Sunni Muslims fleeing the violence who consider ISIS far too extremist. (Ako Rasheed/Reuters)

They consider ISIS far too extremist and fear the violence.

"They are afraid of the fighting that's going on," he said. "They're afraid of the government bombing that has also happened. They're afraid of the government itself, and some of the younger men that I've spoken to have told me that they're afraid of being pulled in for the fighting. Both sides are looking for fighters."

Nearly 300 armed American forces are being positioned in and around Iraq to help secure U.S. assets as U.S. President Barack Obama nears a decision on an array of options for combating the Islamic militants, including airstrikes or a contingent of special forces.

The White House has continued to emphasize that any military engagement remained contingent on the government in Baghdad making political reforms.
 
The U.S. and Iran, Iraq's Shia neighbour and close ally, also held an initial discussion on how the longtime foes might co-operate to ease the threat from the al-Qaeda-linked militants. Still, the White House ruled out the possibility that Washington and Tehran might co-ordinate military operations in Iraq.

The push by the Islamic State's militants has largely been unchecked as Iraqi troops and police melted away and surrendered in the onslaught on the city of Mosul and Tikrit, Saddam Hussein's hometown.

With files from CBC News