With only three weeks left before a deadline to complete a draft of Iraq's new constitution, work stopped Saturday on the toughest unresolved issues in the charter while Shiite and Kurdish politicians tried to end a Sunni Arab boycott of the process, delegates said.

A leading Sunni in the constitution talks, Salih Mutlak, said the Shiites and Kurds had agreed to all but one of his bloc's demands, an international investigation into the assassination Tuesday of a Sunni member of the constitution drafting committee.

The unsolved fatal shooting of Mijbil Esa triggered a walkout by all Sunnis at the talks. Mutlak has accused the Shiite- and Kurdish-led government of a role in the killing. But he said the Sunnis could return as soon as Sunday if the final demand is met.

"We do not want the constitution to be written by others, and we do not want to be away from the political process,'' Mutlak said. "They must act quickly, because if we return late, there is no meaning for our return.''

Lawmakers in Iraq's interim government have committed themselves to having a draft constitution approved by Aug. 15 and a referendum on the document by Oct. 15. Delegates said they must formally notify parliament by Aug. 1 if they are going to miss the deadline.

Finishing the draft constitution on time is seen by U.S. officials and many Iraqis as vital to countering Iraq's insurgents, whose attacks have eroded public confidence in the U.S.-backed government. But including the Sunni minority in framing the constitution is seen as equally important, as a way to draw Sunnis away from the insurgency.

On Saturday, Shiites and Kurds drafting the constitution decided to postpone debate on major unresolved issues, including federalism, said Ali Dabbagh, a Shiite Arab on the constitutional committee.

Kurds and Shiites are urging a strong federal system that would shift power from Baghdad to the provinces, particularly Iraq's Kurdish north and Shiite south.

Jalaladeen Sagheer, a top Shiite member of the constitution committee, said Sunnis wrongly believe federalism is "a step toward the fragmentation of the country."

In an interview in the southern Shiite city of Najaf, Sagheer accused Sunnis of prolonging their boycott in hopes of squelching debate on federalism.

"They say they will not come back until the question of federalism, which is a major demand by the Shiites and the Kurds, is removed,'' the Shiite cleric said. But he said the issue should be resolved "through dialogue and persuasion, not pressure.''

Also Saturday, committee member Bahaa Al Arajy said the committee had rejected a Kurdish demand that the constitution specify a right to a Kurdish vote on independence in eight years. Iraq's northern Kurdistan region already is largely autonomous.

Also Saturday, a statement posted on the internet and attributed to al Qaeda in Iraq, asserted responsibility for kidnapping two Algerian diplomats who were seized at gunpoint in Baghdad Thursday. The attack was the latest of several targeting Middle Eastern diplomats in Baghdad.

Iraq's President Jalal Talabani said some envoys have refused to have Iraqi guards or police escorts. The Iraqi defense and interior ministers will meet Sunday on security issues "including the protection of diplomats and the country,'' Talabani said.

Talabani spoke to reporters at his home alongside the new U.S. ambassador, Zalmay Khalilzad, pledging, "We will cooperate to defeat the terrorists."

"Inshallah, Iraq will succeed,'' Khalilzad said.

Insurgent attacks reported Saturday included the killings of three policemen in Fallujah and the killing of an Interior Ministry employee, news agencies reported.

Correspondent Ellen Knickmeyer in Irbil, and special correspondents Omar Fekeiki and Khalid Saffar in Baghdad, and Saad Sarhan in Najaf contributed to this report.

Iraqi President Jalal Talabani, left, and Zalmay Khalilzad, the new U.S. ambassador to Iraq, speak with reporters after a meeting at Talabani's home.