“Their bodies were torn up to pieces, even their next of kin could not identify them,” an enraged Iraqi soldier said. “It is Iraqi blood, but it is cheap,” he added, pointing to a pool of blood.

The wreckage of motorbikes was piled on the back of a police pickup truck.

Many angry onlookers at the scene said that Iraqi forces were to blame because of their lax approach and infiltration in their ranks by insurgents.

The same Iraqi Army unit is responsible for Nahdha and the nearby Shiite district of Sadr City, where a bombing killed 76 people at a crowded market on Wednesday night.

In Sadr City, hundreds crowded the street outside the local office of Moktada al-Sadr, the anti-American cleric, to attend Friday Prayer and to listen to a sermon given by one of Mr. Sadr’s aides.

In a statement read by the preacher Harith Adthari, Mr. Sadr blamed the Americans for the explosions, saying they bore “the fingerprints of the occupation,” and he urged people to help the loyal Iraqi security forces. He also noted that some infiltrators had penetrated the ranks of the Iraqi forces, and that they must be weeded out.

The prayer, which was attended by larger crowds than in many recent weeks, ended with a spontaneous demonstration in which marchers poured down one of Sadr City’s main streets shouting: “No, no to America. No, no to occupation. No, no to terrorism.”

That was followed by: “Yes for independence. Yes for peace.”

Mr. Sadr’s followers held similar gatherings in the southern cities of Najaf and Basra.

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Although a few people burned a United States flag in Baghdad, the general mood, albeit tense, was less inflamed than it had been at times. Mr. Sadr’s statement counseled his followers to be patient, to pursue “peaceful resistance” and to not give “others the excuse to attack you.” His message to the Iraqi government focused on “forcing out followers of the occupation and Baathists,” members of Saddam Hussein’s former ruling party.

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Afterward people who listened to the sermon seemed certain that the Americans were responsible for the bombing on Wednesday. They also agreed that Sadr City was a safer place when the Mahdi Army militia handled the security.

“All the problems here are American; the whole plan of withdrawal is a game,” said Laith al-Saadi, a pediatrician. “There is no withdrawal. They will still have their agents here, Iraqis and people from neighboring countries.”

Hamid Jassim, 24, interjected: “Before, we protected our own neighborhood and other neighborhoods in Iraq. We have many unemployed young men who can start to take care of this job.” He said they would not do that for now, since the Iraqi security forces were doing that job.

It was unclear though how long the restraint called for in Mr. Sadr’s statement would last, or what it would take to undermine the resolve of Sadrist leaders to keep their movement nonviolent.

“We’ve seen an attack on innocent people in order to stimulate the ethno-sectarian violence that was really a large problem in this country in the last couple of years,” the chief American military spokesman, Brig. Gen. Stephen R. Lanza, told reporters this week. “What’s important to understand is the people have not responded to this.”

He, like other commanders and Iraqi officials, warned of a rise in attacks around the withdrawal deadline, but he said the pace of violence remained on a downward trend.

But Sheik Hamid al-Mualla, a Shiite cleric and member of Parliament, said there were Sunni extremists backed by forces within some neighboring Arab gulf states like Saudi Arabia who were doing their utmost to rekindle Iraq’s sectarian violence.

“I criticize the Arab silence toward the massacres that are happening in our country,” he said in a sermon at Buratha Mosque in Baghdad.

In a statement on Thursday, the prime minister, Nuri Kamal al-Maliki, said Arab states had to take a “clear and definitive stance toward these horrific crimes, because silence is no longer acceptable.”