With only a week until the deadline for a new constitution, Iraqi political leaders launched marathon negotiations Sunday seeking to overcome formidable obstacles blocking agreement on the draft.

Insurgent violence aimed at derailing Iraq's political efforts killed three more American servicemen and at least 13 Iraqi civilians and government employees across the country.

President Jalal Talabani (search), who hosted a first round of constitution talks at his Baghdad home, expressed optimism that leaders from the Shiite, Sunni Arab and Kurdish communities could reach agreement in time for parliament to approve the charter by the Aug. 15 deadline.

Participants said the 21/2-hour meeting produced no breakthroughs, and Sunni Arabs repeated their opposition to transforming Iraq into a federal state — a key demand of the Kurdish minority that wants to protect the self-rule its region has held since 1991.

Saleh al-Mutlaq, a Sunni Arab, said the leaders did manage to prepare a "working program" for a second session Monday afternoon. He would not elaborate.

With divisions deep on such key issues as the role of Islam, federalism and national identity, Talabani acknowledged that agreement would not come quickly. Some Iraqi politicians said intense American pressure would be required to bring all sides together.

Before the meeting, U.S. Ambassador Zalmay Khalilzad (search) urged all the parties to make compromises so Iraq "will serve as a democratic model" for the Middle East and "take its proper place in the international community."

"The United States believes strongly that the Iraqi Constitution should provide equal rights before the law for all Iraqis regardless of gender, race, ethnicity, religion or sect," Khalilzad said in a statement.

Talabani, a Kurd, said the leaders recognized the gravity of the challenge facing them and would exert all efforts to meet the deadline.

"After this meeting, we're going to have continuous meetings and I'm optimistic that we will reach, God willing, positive results," he said. "Eight days are not a little" time.

The Bush administration hopes a new constitution will build political momentum and, over time, lure many Sunni Arabs away from the insurgency, which is rooted in that once-dominant but now discontented minority.

Secretary of State Condoleezza Rice (search) said the insurgency in Iraq was losing steam as a political force.

"If you think about how to defeat an insurgency, you defeat it not just militarily but politically," Rice said in an article appearing on Time magazine's Web site.

Once parliament ratifies the constitution, voters will deliver their verdict in an Oct. 15 referendum. Passage would lead to national elections in mid-December.

If all goes according to plan, the United States envisions being able to begin pulling out some of its 140,000-strong military force in Iraq starting next year.

The effort to produce a constitution is being accompanied by a sharp rise in violence. The U.S. command said Sunday that two Army soldiers and a Marine died in two bombings the previous day. That brought to 30 the number of U.S. personnel killed this month — most by roadside blasts and suicide bombings.

At least 1,828 U.S. military personnel have died since the Iraq war began in March 2003, according to an Associated Press count.

Underlining the insecurity, a U.S. Abrams main battle tank and several Humvees blocked a major street near Talabani's house in the Karradah district as the political leaders talked Sunday night.

The approach of the charter deadline has brought hardened political positions. Shiites insist Islam be declared the main source of legislation, which is opposed by Kurds and many women activists fearing a rollback of their rights. Sunni Arabs, meanwhile, strongly oppose the key Kurdish demand for federalism.

Kurdish leader Massoud Barzani has threatened to bolt the political process if Kurdish positions are not included in the new charter. Barzani, head of the Kurdistan Democratic Party (search), had planned to attend the Sunday talks but was delayed by sandstorms.

About 1,000 protesters angry with the lack of clean water and electricity clashed with Iraqi police in the southern city of Samawah, where Japanese troops are based. One person was killed and about 60 were injured, police said. The protest was organized by radical Shiite clerics demanding that all foreign troops leave the country.

A suicide bomber detonated an empty fuel tanker near a police station in Saddam Hussein's hometown of Tikrit, killing at least two people and injuring at least 13, police said.

Three Iraqi soldiers and two Oil Ministry employees also were killed in two separate drive-by shootings in Baghdad.

In Baghdad, three Iraqi soldiers dressed in civilian clothes were gunned down while heading to work, said Dr. Muhannad Jawad of Yarmouk Hospital. A fourth soldier was wounded.

Assailants opened fire and then threw a grenade at a police vehicle in the central Iraqi city of Baqouba, killing one policeman. One civilian was also killed and three policeman were wounded in the attack, police said.

In southern Basra, gunmen in two speeding cars killed a policeman.

Al-Jazeera television aired a video of what it said were three Turkish truck drivers kidnapped in Iraq, reportedly while working for a company that transports supplies for U.S. forces. Insurgents have kidnapped more than 200 foreigners seeking to discourage help for the Iraqi government.