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Abdul-Hadi al-Hassani, a member of parliament from Mr. al-Maliki’s Dawa Party, said that “the Shi’ites have limited patience, but what happened lately has proved that they want to prevent Iraq from getting dragged back to the sectarian conflict.”

“If this does happen,” he added, “it would burn everything. It would take the political process back to zero.”

Still, the violence is unsettling. Last Wednesday night in Baghdad’s Shula neighborhood, a driver parked on the side of a popular street lined with restaurants and an ice-cream parlor before disappearing among the evening shoppers and diners. The car exploded, sending metal shards and fire through the crowds, killing more than 40 people and injuring more than 70, according to local police.

On the following morning, two more explosions shattered the calm in Baghdad, and a third occurred in the northern city of Kirkuk. At least 25 Iraqis were killed, as were three members of the U.S. military.

In two of the incidents, suicide bombers were to blame. They blended in by wearing the uniforms of Iraqi security forces.

Anthony Cordesman, a national security and Middle East specialist at the Center for Strategic and International Studies in Washington, said, “People throughout the Iraqi security forces have often left their jobs without becoming any kind of insurgent or fighter, but in the process, they sell what they take with them, which includes their uniforms. This makes it extremely difficult to figure out who is in and who is out.”

“You could not secure Washington, D.C., against this kind of suicide bombing,” Mr. Cordesman added. “You could protect individual facilities, but if people are going to assemble in parks or any other public place, the reality is that every society remains vulnerable.”

Gen. al-Jaberi suggested one possible solution. “Since many security forces have been infiltrated by al Qaeda, I have suggested that all checkpoints must be manned by both the Iraqi Army and the local police,” he said. “That way, we will watch each other, and will be able to know who is working for the country, and who is working for the bad people.”

Yousif al-Timimi contributed to this report.