Sahwas helped curb violence in Iraq after they turned against al-Qaeda and other anti-government groups.
The Baghdad government took full responsibility for paying them at the start of the month and has promised to absorb 20 per cent of the 92,000 fighters into the regular security forces. Others have been promised government jobs or training.
Relations between the Sahwas, also known as Awakening Councils, and the government in Baghdad led by Nuri al-Maliki have been strained in recent weeks by the arrest of Sahwa leaders.
There has also been tension over a delay in salaries being paid to the Sahwas in recent weeks, sparking concerns that the government could disband them.
"This was the third time we had come to get our salaries, because they postponed the payment the first two times," one Sahwa member wounded in Saturday's attack told the AFP news agency, asking not to be named.
The suicide attack came at the end of a particularly deadly week in Iraq, where a series of bombings killed 70 people and wounded more than 300.
In a suicide truck bomb in the northern city of Mosul, five US soldiers and three Iraqi security forces were killed on Friday.
The Mosul bombing was the deadliest attack on American forces in more than a year and underscored the problem of maintaining security in some areas of the violence-wracked nation.