BAGHDAD (Reuters) – A suicide car bomber killed six members of an anti-al Qaeda tribal police unit when he struck their checkpoint near Baghdad on Monday, police said.

Police said several others were wounded in the attack near Balad, 80 km (50 miles) north of the Iraqi capital.

It was the latest attack on members of the Salahuddin Awakenings Council, an alliance of tribes in the Sunni Arab province of Salahuddin opposed to al Qaeda’s religious extremism and its indiscriminate killing of civilians.

Similar councils have been established in Anbar and Diyala provinces. The U.S. military has signed up hundreds of tribesmen and even members of Sunni Arab insurgent groups to form “concerned citizens” groups to battle al Qaeda.

They have enjoyed their greatest success in Anbar, once thought lost to al Qaeda and the most dangerous place in Iraq for U.S. troops. Since the tribes turned against al Qaeda, violence has subsided dramatically in Anbar.