Members of the Sunni anti-Al-Qaeda militia Sahwa (Awakening) patrol a flooded area during operations to fight against ISIS.

At least 33 people were killed near the Iraqi capital of Baghdad on Wednesday when a suicide bomber attacked fighters opposed to Islamic State of Iraq and Syria militants, officials told Reuters news agency.

The attack on the fighters, known as Sahwa or the “Awakening Councils,” occured near a military base in the Madain area.

According to the Associated Press, the attacker managed to mingle with the militiamen who had gathered to receive their monthly payment, two police officers said.

At least 15 of the dead were Sunni militiamen and the rest were soldiers, while 55 others were wounded, they said.

The town is located about 20 kilometers south of Baghdad.

The group is made up of Sunni militiamen who joined U.S. troops in the fight against al-Qaida during the height of Iraq’s insurgency in 2007 and 2008. They are viewed as traitors by the Sunni militants.

Three medical officials confirmed the casualty figures. All officials spoke on condition of anonymity as they were not authorized to release information to the media.

No one immediately claimed responsibility for the bombing, but it bore the hallmark of the Islamic State group, which captured large swaths of western and northern Iraq in a summer blitz. The militant group’s onslaught has become Iraq’s worst crisis since the 2011 withdrawal of U.S. troops.

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