Updated

A spokesman for the biggest Shiite (search) party Thursday predicted a breakthrough on the constitution within the next two days, as negotiators scrambled to finish the draft by next week's deadline.

On Thursday, a roadside bomb killed four more U.S. soldiers in a city north of Baghdad.

Four days before the deadline, Sunni Arab members of the drafting committee met with Prime Minister Ibrahim al-Jaafari (search) to present their objections to federalism and other issues blocking an agreement.

Afterward, leaders of the factions — Shiites, Sunni (search) Arabs and Kurds (search) — conferred late into Thursday night at the home of Vice President Adil Abdul-Mahdi (search) in the heavily fortified Green Zone. No statement was issued after the meeting, but representatives of all three factions spoke optimistically about prospects for finishing by the new deadline Monday.

Parliament voted unanimously last Monday to extend the deadline by one week after negotiations deadlocked over a number of issues including federalism, Kurdish demands for the right to secede, distribution of oil wealth and the role of Islam.

The interim constitution states that the legislature must dissolve if the negotiators cannot finish their work by the new deadline.

But Haitham al-Husseini, a spokesman for the Supreme Council for the Islamic Revolution in Iraq, said he expected a breakthrough within 48 hours, adding that "the work is being done in an inclusive way to overcome the points of disagreements."

Similar optimism was expressed publicly last week before the negotiators had to admit they were deadlocked. However, Sunni and Kurdish officials also seemed upbeat.

"I expect that the constitution would be finished before Monday," Sunni negotiator Saleh al-Mutlaq said. "Negotiations are still under way and everybody is determined to finish it before the deadline."

He said American and British officials were pressing the Sunnis to compromise on the issues of federalism and other topics.

"Americans are more concerned about the sacred deadlines rather than the contents of the constitution," al-Mutlaq said.

However, both the Shiites and the Kurds again pointed to the Sunnis as the main holdouts because of their opposition to transforming Iraq into a federated state, which they fear would lead to the breakup of the nation.

The Sunni Arabs would likely gain strength in parliament if the legislature were forced to dissolve over the constitution issue because many of them boycotted the January election and Sunni candidates fared poorly.

Sunnis have signaled they would participate in a new election.

Mahmoud Othman, a Kurdish lawmaker, said all sides were determined to finish the constitution on time "but the question is, would this draft satisfy the Sunni Arabs' demands."

But he also said that if the Shiites and Kurds reached agreement, they would submit the constitution to parliament on time, even if the Sunnis disapprove. The Shiite and Sunni parties control 221 seats in the 275-member parliament.

Othman said the triple bombings Wednesday that killed up to 43 people in Baghdad "encourages the political leaders to finish the job as well as present compromises."

"The people are suffering and they should be respecting the people's will," he added.

Government spokesman Laith Kubba said the bombers Wednesday targeted a neighborhood that is populated mostly by people who moved here from southern Shiite provinces. Kubba also said four suspects detained shortly after the attacks had been released after questioning.

Kubba said fliers recently had been handed out in some Baghdad neighborhoods threatening Shiites if they did not leave the city. At least one person, a Sunni Arab woman married to a Shiite, had been killed after the threats, he said.

"Their message was that their government is unable to protect you from us," Kubba said. "They want a reaction against Sunnis to therefore deepen the sectarian crisis in the country."

The United States is eager for the Iraqis to finish the constitution as a major step in a political process which the Americans hope will, in time, lure disaffected Sunni Arabs away from the insurgency.

That would enable the United States and its international partners to begin drawing down their forces next year.

However, U.S. officials had also placed great hopes on other milestones — the December 2003 arrest of Saddam Hussein, the June 2004 handover of sovereignty and the Jan. 30 elections. Yet the insurgency continues.

The four American soldiers died in a bombing in Samarra, a religiously mixed city 60 miles north of the capital, the U.S. military said. No further details were released.

At least 1,864 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count.

Samarra was among a number of towns and cities that fell under insurgent control last year after the transfer of sovereignty. The U.S. military regained control of Samarra last year but the situation there remains tense.

The top U.S. commander in the Middle East, Gen. John Abizaid (search), discussed the security situation Thursday with President Jalal Talabani (search) and afterward said U.S. and Iraqi forces would "continue the fight against these people that are killing innocent Iraqis day after day after day for no reason other than to try to grab the headlines."

"We must fight the terrorists together so that we can have a free and prosperous future for the Iraqi people," Abizaid said.

Gen. George Casey (search), the senior U.S. commander in Iraq, identified "foreign fighters and the Iraqis that support them" as the greatest threat to Iraq over the next six months to a year.

"They are the ones that are killing Iraqi people on a daily basis," Casey said. "We are focusing our military operations against them."