Newly-recruited Iraqi volunteers take part in a training session in Karbala.

BAGHDAD: Police said Tuesday that pro-government Shiite militiamen killed nearly four dozen Sunni detainees after insurgents tried to storm a jail and free them northeast of Baghdad. The Iraqi military, however, insisted the inmates were killed when the attackers shelled the facility.

Neither account could be independently confirmed, but the allegation of Shiite killings of Sunnis was the first hint of a possible return to past sectarian warfare that nearly tore the country apart.

The insurgents were repelled, but the fighting around the jail outside Baqouba was the closest to Baghdad since the Al-Qaeda breakaway group the Islamic State of Iraq and the Levant began its lightning advance, seizing several key cities in the Sunni heartland in northern Iraq.

There were conflicting details about the fighting in the Al-Kattoun district near Baqouba, the capital of Diyala province and one of the bloodiest battlefields of the US-led war, and on how the detainees were killed. The city is 60 km northeast of the Iraqi capital.

Three police officers said the police station, which has a small jail, came under attack on Monday night by militants who tried to free the detainees, mostly suspected Sunni militants. The three said Shiite militiamen, who rushed to defend the facility, killed the detainees at close range. A morgue official in Baqouba said many of the slain detainees had bullet wounds to the head and chest. All four officials spoke on condition of anonymity fearing for their own safety.

However, Iraq’s chief military spokesman Lt. Gen. Qassim Al-Moussawi, told The Associated Press that 52 detainees who were held at the station in Al-Kattoun died when the attackers from the Islamic State shelled it with mortars.

The group is known to be active in Diyala, a volatile province with a mix of Sunnis, Shiites and Kurds and where Shiite militiamen are deployed alongside government forces.

Nine of the attackers were killed, Al-Moussawi said.

The conflicting reports could not immediately be reconciled, but if the version of events provided by the policemen and the coroner is independently verified, then the incident would be an example of the sectarian strife and atrocities Iraq’s ongoing crisis could yield.