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.