BAGHDAD, Iraq - Iraqi Kurds will never back down from demands for a federal state despite problems this may create in efforts to draft a new constitution, a top Kurdish leader said today. U.S. officials pressed Iraq to meet the deadline for completing the charter.

Massoud Barzani, head of the Kurdistan Democratic Party, also said Kurds would never dissolve their militias and repeated demands for the return of ethnic Kurds to the oil-rich Kirkuk area from which tens of thousands of them were expelled under Saddam Hussein.

Barzani's comments, broadcast by Al-Arabiya television, indicated the Kurds are standing firm on longtime demands at a time when the United States is urging all sides to compromise in order to finish the new constitution by the Aug. 15 deadline.

His remarks were broadcast as Defense Secretary Donald Rumsfeld arrived in Baghdad to urge the Iraqis not to miss the deadline for completing the draft of the constitution. The Defense Department wields considerable influence among the Kurds, who worked closely with the Americans in preparations for the 2003 invasion that toppled Saddam.

"It's time for a compromise. That's what politics are about and people are simply going to have to recognize that (in) any constitutional drafting process, compromise is necessary. It's important. It's understandable. It's the way democratic systems work," Rumsfeld said.

At a joint press conference with Rumsfeld, Prime Minister Ibrahim Jaafari said the time has arrived to plan a coordinated transition from American to Iraqi military control throughout the country.

Asked how soon a U.S. withdrawal should happen, he said no exact timetable had been set. "But we confirm and we desire speed in that regard," he said, speaking through a translator.

Speaking earlier with U.S. reporters traveling with Rumsfeld, Gen. George Casey, the top American commander in Iraq, said he believed a U.S. troop withdrawal could begin by spring 2006 if progress continues on the political front and if the insurgency does not expand.

In ongoing violence, mortar attacks on Baghdad's main bus station today killed at least two and injured 20 others, said Dr. Muhannad Jawad of Yarmouk Hospital. Most of the victims are believed to be Iraqi civilians.

South of Baghdad, insurgents fired a number of mortar rounds on an Iraqi military base, leaving another 10 people injured, including six soldiers, said Dr. Dawood al-Taie, director of the Mahmoudiya hospital.

A statement released Tuesday by the U.S. command said a roadside bomb had killed four American soldiers in southwestern Baghdad. The statement said the soldiers from Task Force Baghdad died Sunday night when their vehicle ran over a roadside bomb in the southwest of the city.

However, Jim Driscoll, a spokesman for the Georgia National Guard, said the victims were assigned to the 48th Infantry Brigade. They were the Georgia Guard unit's first combat casualties since World War II.

Seven Iraqi soldiers were shot and killed as they were guarding a water plant in the town of Tarmiyah, the Defense Ministry said today. Insurgents have frequently attacked water and electricity plants in a bid to further destabilize the country.

Preliminary drafts of the Iraq's constitution call for disbanding all militias associated with Iraqi parties since the days when they were fighting Saddam. The Kurds have long maintained that their peshmerga fighters are not a militia but rather the security force of their autonomous Kurdish region in the north.

However, it is unlikely that the Shiites and others would accept an end to their own militias if the Kurds are allowed to keep their peshmerga fighters.

"The peshmergas will stay and there is no force that will be able to cancel them," Barzani said.