“The blast threw me to the ground and shattered a window over my body,” said Salar Kamal Zari, a 37-year-old teacher visiting from Kurdistan, who had just stepped into a nearby store when the bomb exploded. “I saw a human head in front of the store and many cars burning and smoke everywhere.”

“I will never stay in Baghdad anymore,” he vowed.

The Baghdad security plan calls for 28,000 additional American troops, as well as thousands of Iraqi soldiers, most of whom will be deployed in the streets of the violent capital in an attempt to pacify it. But Mr. Maliki said the gradual handover to Iraqi authority would continue, with three provinces in the relatively tranquil region of Kurdistan the next to come under Iraqi security authority, followed by Karbala and Wasit Provinces in the south.

“In this way, province by province, we will reach the end of the line before the end of the year,” the prime minister said in a speech delivered by Mowaffak al-Rubaie, his national security adviser. The speech marked the handover of the southern province of Maysan from British to Iraqi control. Maysan is the fourth of Iraq’s 18 provinces to be handed to Iraqi security forces.

American commanders have said the Baghdad security effort has reduced the kinds of sectarian killings associated with Shiite death squads, in part because of the decision by many militia fighters to lay low.

But the plan has failed to curb the spectacular attacks, many of them suicide bombings, that have become a gruesome hallmark of the Sunni Arab-led insurgent group Al Qaeda in Mesopotamia. As a result, commanders say, overall civilian casualty rates are actually higher now than they were before the plan was initiated.