Several people were wounded Thursday when Iraqi police clashed with members of an Iranian-backed militia near the capital, both sides said.

The violence in Zaafaraniya, south of Baghdad, involved exchanges of fire that lasted more than two hours between police forces and the Harakat al-Nujaba group.

"The clashes started when the security forces arrested a member of Harakat al-Nujaba, whose forces then attacked a police base to release him," a police colonel said.

The officer said a policeman and a civilian were wounded and added that the detained senior member of the Shiite militia was still being held.

The group, a splinter of the powerful Asaib Ahl al-Haq militia, is part of the Hashed al-Shaabi paramilitary organisation that has played a key role in the fight against the Islamic State jihadist group.

Harakat al-Nujaba gave a markedly different account of the clashes and accused the police of collaborating with IS.

It said in a statement posted on social media by its spokesman Nasr al-Shammari that one of its intelligence cells had arrested an IS commander after "tracking him for three months in cooperation with the security services."

It said the Nujaba force was then stopped at a checkpoint and asked by the police to report to a nearby base and officially record the arrest.

"When they arrived at the base, they arrested the (Nujaba) force and released the Daesh (IS) commander," Shammari said.

He said Nujaba forces that arrived at the base later were shot at by the police, adding that three of them were seriously wounded.

Shammari said the incident in Zaafaraniya was evidence police were colluding with IS and that "the situation in the country will not be stable until the security apparatus has been purged".

The Hashed al-Shaabi -- "popular mobilisation" in Arabic -- is nominally under the authority of the prime minister but the allegiance of some of its most powerful components is first and foremost to Iran.

Harakat al-Nujaba, which was formed in 2013 and led by Akram al-Kaabi, is believed to have strong ties with Lebanon's Hezbollah organisation and is known for taking part in operations in neighbouring Syria.