Shia militant jihadists fighting under the banner of the Popular Mobilisation Forces (PMF) in Iraq have shelled military outposts and positions belonging to the Kurdish Peshmerga militia, despite both factions being technically allied in a US-backed offensive to retake Mosul from Daesh militants.

Kurdish officials confirmed the attack on Peshmerga positions in the Sinjar area yesterday, west of Mosul in northern Iraq and near the border with war-torn neighbour Syria.

Sinjar lies on one of the main roads that connect Iraq to Syria, and is currently militarily occupied by Shia militants, Peshmerga and even extremist leftist groups such as the Kurdistan Workers’ Party (PKK), which has caused concern in neighbouring Turkey.

Halgurd Hikmat, a media spokesman at the Peshmerga Ministry, part of the autonomous Kurdistan Regional Government (KRG) in northern Iraq, said in comments to Kurdish news outlet Rudaw that the incident was “not the first time such things are happening [sic].”

“We are awaiting an official response from the Hashd Al-Sha’abi regarding the incident,” Hikmat said, using the Arabic term for the PMF militants.

This morning, the PMF announced that it had opened an investigation into the shelling of its Kurdish allies, describing the incident as a “mistake”.

“We have formed a quick investigative committee to determine the circumstances of what happened and to prevent such mistakes,” the PMF’s spokesman Ahmad Al-Assadi said in a statement, adding that these incidents “do not help the course of the battles [against Daesh or] continue the series of victories.”

Al-Assadi also said that a joint committee between the PMF and Kurdish Peshmerga had been set up to investigate the incident in Sinjar, noting that both paramilitary organisations are stationed quite close together. This raises the question of how closely positioned units could accidentally fire on each other.

Nevertheless, the PMF’s spokesman concluded by saying: “The Peshmerga is part of the Iraqi armed forces. They are our brothers, and essential partners in…defeating the terrorist Daesh. There are close outposts between the Peshmerga and the Hashd [PMF] in the area, and there is high coordination between the two sides.”