BAGHDAD, Iraq — A suicide bomber rammed his truck into a police station in a town south of Baghdad on Friday, killing four police officers and one civilian.

The attack took place in Yousifiya, about 10 miles outside the capital, in an area once dubbed the “triangle of death” because of the level of Sunni Muslim insurgent violence. In the past year, however, violence there has subsided considerably.

U.S. officials have credited the turnabout in large part to the recruitment of former backers of the insurgency, often referred to as Concerned Local Citizens, who now work as volunteers alongside U.S. and Iraqi security forces.

The leader of the largest Shiite Muslim party in Iraq’s Parliament warned Friday against giving too much power to the mainly Sunni volunteer security forces, which are the backbone of a U.S. push to stabilize the country.

Abdelaziz Hakim is a key U.S. ally in Iraq, but his comments about the so-called Awakening councils underscored the sensitivity of the issue as U.S. officials increase pressure on Iraq’s government to give jobs to their members.

Americans pay the volunteers about $10 a day, and most volunteers hope to get jobs as Iraqi police officers.

“We highly appreciate the role of the Awakening … in their pursuit of terrorists,” said Hakim, who leads the Supreme Iraqi Islamic Council. He went on to say the councils should “continue in their supportive and assistance role” but not become a substitute for the security forces.

“Weapons should only be in the hands of the government,” Hakim said.

The future of the estimated 70,000 volunteers probably will become a sticky issue as the U.S. begins lowering its troop levels in Iraq. Now that violence is down nationwide, the 28,500 extra American troops deployed this year are starting to be withdrawn. That puts greater emphasis on the Iraqis to sustain security gains by bolstering their security forces.

If the volunteers are not given jobs, though, concerns exist that they may turn on both U.S. and Iraqi forces.