Greeting each other with handshakes and embraces, some of Iraq's most powerful Shiite and Kurdish leaders gathered Sunday at a private resident in Baghdad in an effort to hammer out disputes that threaten to block completion of a national constitution by the Aug. 15 deadline.

"I am optimistic that we will achieve solutions that will be agreed upon by all," said President Jalal Talabani, a leader of the transitional government elected to draft the constitution. "We still have a week ahead, and when you multiply the number of hours in this week, you will see we have enough time."

The meeting of the pivotal leaders, who arrived in cavalcades of sport-utility vehicles with tinted windows, came on a day when political violence claimed about a dozen Iraqi and U.S. lives. The bloodshed heightened Iraqi and U.S. concerns that a failure by the interim leaders to pull together a cohesive government and charter by the deadline could expose the country to greater unrest.

U.S. leaders have urged the Iraqi leaders to stick to a schedule that would mandate the completion of the draft constitution by next week, a national vote on the charter in mid-October and new national elections by December, keeping alive the U.S. goal of beginning major troop withdrawals in the spring.

A legislative commission drafting the charter has been split on several matters, including the role of Islamic law and the extent of autonomy that the Kurdish north and the Shiite south should be allowed.

Several key leaders were absent from Sunday's meeting, including Moqtada Sadr, a Shiite cleric who has rejected participation in the process as long as U.S. forces remain in Iraq. Massoud Barzani, leader of a Kurdish faction that has aggressively upheld Kurdish territorial claims and the right to decide on independence from Iraq, also did not attend. Talabani's aides said sandstorms had grounded Barzani's helicopter.

Sunni Arab leaders, whose disgruntled minority supplies most of the fighters for the insurgency, are expected to meet separately on Monday. All factions are slated to assemble on Tuesday.

The violence Sunday included a bombing west of Baghdad that killed a Marine, the U.S military said. No details were available.

In central Iraq earlier in the day, a suicide bomber driving an empty fuel tanker detonated explosives near a police station, killing at least two Iraqi policemen, police told news agencies.

Assailants opened fire and then threw a grenade at a police vehicle in the central Iraqi city of Baqubah, killing one policeman and one civilian.

In Basra in the south, gunmen in two cars killed a policeman. Also in the south, a region generally calmer than central Iraq, police fired on hundreds of protesters blaming the U.S. presence for shortages of electricity and water. One person was killed and about 60 were injured, police told the Associated Press.

In Baghdad, three Iraqi soldiers in civilian clothing were gunned down on their way to work, a doctor at Yarmouk Hospital told the AP. And north of Baghdad, two Oil Ministry employees were killed when gunmen fired into their vehicle, police told news agencies.

Special correspondent Omar Fekeiki contributed to this report.