The violence poses a significant threat in provinces where both forces operate, where it could inspire further unrest.

Clashes between Iraqi Kurdish and Shiite fighters north of Baghdad killed seven people Thursday, an official said, illustrating major fault lines between ostensible allies against the ISIS militant group.

The violence poses a significant threat in provinces where both forces operate, where it could inspire further unrest.

The fighting killed seven people and wounded 22, including civilians as well as combatants, said Shallal Abdul Baban, the local official responsible for the area.

Some 40 people from both sides have been detained in connection with the unrest, he said.

The violence began at a checkpoint near the town of Tuz Khurmatu and then spread inside it, and led to the closure of the main road linking Baghdad with the autonomous Kurdish region.

Gunmen from both sides took up positions in buildings in the town and used automatic weapons and rocket-propelled grenades in the fighting, said Ridha Mohammed Kawthar, the head of the local security committee.

A curfew was announced due to the violence, Kawthar said, and Baban said the fighting had stopped by Thursday evening.

Kurdish officials blamed Shiite fighters for the start of the violence, saying they refused to stop at a checkpoint, leading to a dispute that escalated into clashes.

But Mohammed al-Bayati, a leader in the Badr militia, said a group of Shiite fighters including some of his group’s forces were attacked by Kurdish forces “for no reason”.

Iraqi Kurdish forces and members of the Popular Mobilisation units, which are dominated by Iran-backed Shiite militias, have been two of the most effective forces in the battle against ISIS, which overran large parts of the country last year.

But while both forces are opposed to the militants and have cooperated at times, they differ sharply in their loyalty and aims.

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