BAGHDAD, May 8 — The threat of a walkout by Iraq’s leading Sunni bloc in Parliament and the cabinet seemed to subside Tuesday after a meeting between Prime Minister Nuri Kamal al-Maliki, a Shiite, and Vice President Tariq al-Hashimi, a Sunni.
But violence in Iraq continued. A suicide car bomber killed at least 16 people near the main mosque in Kufa that Moktada al-Sadr has used to deliver his Friday sermons. It was the third car bombing in a month near a revered Shiite shrine in southern Iraq.
And residents in Baquba said an American helicopter fired on a group of students, killing as many as seven. Lt. Col. Christopher Garver, a military spokesman, confirmed that there was helicopter activity in the area and said that the accusations were being investigated.
The United States military also announced that two soldiers died Tuesday when a roadside bomb struck their vehicle southeast of Baghdad.
Mr. Hashimi threatened Monday to lead a Sunni boycott by next week unless there was a clear move to change the Constitution so that the country could not be partitioned into separate Shiite, Sunni and Kurdish states — which the Sunnis fear largely because the country’s oil wealth is concentrated in Shiite and Kurdish areas.
Though he has not formally rescinded the threat, Mr. Hashimi seemed eager to show that he was willing to cooperate. His office released a picture of him with the prime minister sitting side by side and smiling, as well as a statement saying that the meeting had moved the political process forward.
“The vice president appreciated the clear and friendly feelings that filled the meeting,” the statement said.
Reform of the Constitution is one of several benchmarks that American officials are pushing the Iraqi government to meet.
They hope changes in the document would form the foundation for a stable government that more equitably divides resources and responsibilities among the country’s three main factions. The issue of whether to prevent partition — as Mr. Hashimi wants — is just one of many being discussed.
Mr. Hashimi’s threat of a walkout and his meeting with the prime minister suggest that pressure for compromises on the Constitution is mounting, not just in the United States but also here.
A deadline looms: the parliamentary committee dealing with proposed amendments to the Constitution is scheduled to deliver recommendations next Tuesday. Parliament will then debate the proposals and vote.
It remains unclear, however, whether Sunni, Shiite and Kurdish politicians are close to an agreement. Three members of the 31-member constitutional committee said Tuesday that the recommendations would probably not address the most contentious issues, such as how to share water, oil and other resources.
Nicholas Hayson, a constitutional adviser for the United Nations who has worked closely with the constitutional committee, said, “It may well be that the committee will need more time to put together compromises that all communities can live with.”
Punctuality in politics here tends to be rare. Iraqi leaders have missed several deadlines during the constitutional reform process. They have recently complained that the American deadlines for compromise are unrealistic.
The car bomb in Kufa was just the latest illustration of the relentless security challenge that Iraq’s government faces. The blast disintegrated vendor stalls and bloodied shoppers.
Observers said that security in the Shiite-majority south, home to the holy cities of Najaf and Karbala, seemed to be deteriorating.
“A lot of people are angry because the government is incapable of preventing such attacks,” said Ahmad Yasir Hussein, 33, the owner of a grocery store near the explosion site.
The driver of the vehicle, a Chevrolet Caprice packed with more than 550 pounds of explosives, moved into the market area around 10 a.m., the police said. Capt. Hadi Najim, the head of the explosives removal bureau in Kufa, said only half of the explosives in the car detonated.
Hussein Abed Matrood, 38, said he had just parked his car near the market when the force of the explosion reached him.
“I was hit with shrapnel and my wife’s leg was broken,” he said. “Thank God, my son was left intact. He stayed in the car.”
After the bombing, cars were banned from downtown Kufa and Najaf, the adjacent city and home to one of Shiite Islam’s holiest shrines, according to Ahmed Duaibil, head of the news media office for the governor of Najaf Province.
Ahmad al-Fatlawi, a member of province’s governing council, said the area has come under attack because it is thriving while Baghdad and other areas struggle.
“The terrorist groups target the stability in Iraq generally, and Najaf specifically, because the reconstruction wheel is still going forward and this doesn’t serve terrorism,” he said. “These groups try to stop this wheel with such acts, and to hinder the process and to create chaos. This will not happen — construction will continue.”
In Baghdad, aides to Mr. Maliki and Mr. Hashimi also tried to sound upbeat. Mariyam al-Rais, an adviser to the prime minister, said the possibility of a Sunni departure from the government had always been “illogical” and unlikely. Ms. Rais said the prime minister’s meeting with Mr. Hashimi covered several points of disagreement.
In a particularly ambitious effort to gild Iraq’s struggles, she also touted the criticism of Mr. Maliki from both Shiites and Sunnis as a sign of the government’s impartiality.
“No side in the political process agrees totally with the government’s performance, which makes the government really fair and not biased to any side,” she said.