A suicide bomber has attacked Sunni fighters opposed to the Islamic State in Iraq and the Levant (ISIL) group as they gathered to receive salaries in an area south of Baghdad, killing at least 38 people, according to Iraqi officials.

Wednesday's attack on the members of the Sahwa (Awakening) movement near a military base in the Madain area also wounded at least 56 people, officials said.

The Sahwa date back to the height of the US-led war in Iraq in 2000s, when Sunni tribesmen joined forces with the Americans to battle fighters including ISIL's predecessor organisation, Islamic State of Iraq.

The Sahwa were key to sharply reducing violence, but when Iraq's government took over responsibility for their salaries they were sometimes paid late or not at all.

Sunni fighters, including the Sahwa and other armed tribesmen, fight against ISIL too.

The Iraqi government has distributed arms and ammunition to tribesmen, and Haider al-Abadi, prime minister, aims to establish a national guard made up of local fighters, though the necessary law has yet to pass parliament.