Sunni volunteers carry weapons during a parade as they prepare to fight against militants of the Islamic State, in the town of Amriyat al-Falluja in Anbar province.

Iraq’s prime minister said on Saturday he had ordered an investigation into the killing of two Sunni Muslim civilians at a security headquarters in Anbar province, where the army and volunteers are battling ISIS insurgents.

Haider al-Abadi, a moderate Shiite Islamist who took office in September, is keen to show his government is accountable to all of Iraq’s sects and to mend the rifts ISIS was able to exploit when it seized parts of the country last year.

Local officials, a tribal leader and an army officer said two men from a prominent Sunni tribe were killed at the Anbar Operations Command earlier on Saturday after being detained at a checkpoint operated by security forces along with Sunni and Shiite volunteer fighters.

Abadi announced the investigation on his official Facebook page, calling the killing “a heinous crime… intended to sow discord and distract (citizens) and the security forces from fighting the Daesh (a reference to ISIS) criminal gang.”

A myriad of pro-government forces are fighting against ISIS in Anbar, including Shiites and Sunnis, who have come to resent the brutality of ISIS rule.

Shiite militias and government-supervised volunteers known as Hashid Shaabi have led efforts to stop ISIS from overrunning Baghdad since the Iraqi army nearly collapsed last summer.

“These men were innocent. They were driving a car that had license plates from Saudi Arabia and they were stopped by the Hashid Shaabi, taken to the Anbar Operations Command and executed there by having their throats slit,” Sabah Karhut, Anbar provincial council chief, told Reuters.

Abadi’s spokesman declined to provide details about the incident or the promised investigation.

Abadi called for an investigation last week into accusations that Shiite militias systematically killed at least 72 people in the eastern village of Barwanah.

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