Clashes erupted between the Iraqi federal police and Iran-backed militias in Mosul on Sunday.
A gun battle began when Iraqi police stopped the militias entering western Mosul. Two police officers were injured.
The militias, also known as Hashed Al Shaabi, were formed in 2014 to assist Iraqi forces defeat ISIS but are accused of exploiting their position and human rights breaches.
They took up positions in and around Mosul after the country declared victory against ISIS in 2017.
But areas that contain the Iraqi police and militia members in Mosul have been tense because of the overlap of duties between the two.
“Police members prevented the Hashed entering one of the neighbourhoods in western Mosul where protests against poor public services had taken place,” a local security official said.
“Security members blocked the Hashed from entering the area because it did not fall within their jurisdiction and their line of duty."
The protesters were demanding basic rights that they say members of the Hashed had denied them, the official said.
The increasing influence of the Hashed, whose most powerful factions are backed by Iran, is worrying the US as tension mounts with Tehran, which is securing its influence over a corridor of territory through Iraq and Syria to Lebanon.
The militia are regarded by the US as among the biggest threats to the region’s security. They are supported and trained by Tehran.
Last week, Washington designated Iran’s Islamic Revolutionary Guard Corps a terrorist group to highlight Tehran’s efforts to destabilise the Middle East by supporting armed groups.
Tension escalated between the two after US President Donald Trump withdrew from an international nuclear pact and imposed economic sanctions on Tehran last year.
Iran spends nearly $1 billion a year to support terrorism, a State Department official told The National last week.
“It continues to provide funding to many designated terrorist groups in Iraq, including Kata’ib Hezbollah and Harakat Al Nujaba,” the official said.
He said Iran was responsible for the deaths of 603 US personnel in Iraq.
In response to the designation for the IRGC, the militias in Iraq said they strongly rejected Washington’s decision. They announced solidarity with the Guards.
Some of the militia groups are also designated terrorist organisations by Washington.