BAGHDAD — Iraq's chief spokesman acknowledged differences with the U.S. over a proposed long-term security agreement and pledged Sunday that the government will protect Iraqi sovereignty in ongoing talks with the Americans.

Australia became the latest member of the U.S.-led coalition to pull combat soldiers from Iraq, fulfilling an election promise that helped sweep Prime Minister Kevin Rudd to power in November.

Opposition has been growing in Iraq to the proposed security pact with the U.S., which will replace the current U.N. mandate and could provide for a long-term American military role in this country.

Much of the opposition comes from anti-American Shiite cleric Muqtada al-Sadr, but statements critical of the deal have also been issued by mainstream Sunni and Shiite figures who fear it will undermine Iraqi sovereignty.

Chief government spokesman Ali al-Dabbagh said the Iraqi negotiators have a "vision and a draft that is different" from the Americans but that the talks, which began in March, were still in an early stage.

"There is great emphasis by the Iraqi government on fully preserving the sovereignty of Iraq in its lands, skies, waters and its internal and external relations," al-Dabbagh said. "The Iraqi government will not accept any article that infringes on sovereignty and does not guarantee Iraqi interests."

U.S. officials have refused to comment on the talks until they are complete but have insisted they are not seeking permanent bases. The agreement is to replace a U.N. mandate for U.S.-led forces that expires at the end of the year.

President Bush and Iraqi Prime Minister Nouri al-Maliki said they were hoping to finish the negotiations by July to allow time for the Iraqi parliament to sign off on the deal.

But Iraqi officials said last month that talks were unlikely to wrap up by July because of wide differences over several issues, including immunity enjoyed by U.S. troops from prosecution in Iraqi courts and rules governing U.S. military operations.

In recent weeks, Iraqi forces have taken the lead in operations against Al-Qaida in Iraq and other Sunni militants in the northern city of Mosul and against Shiite militias in southern Basra and in the Shiite district of Sadr City in Baghdad.

But the government appears to be following a policy of negotiating with militants — a strategy that calmed the situation in the three cities but probably enabled some hardliners to slip away to fight another day.

During a press conference Sunday, Foreign Minister Hoshyar Zebari, a Kurd, spoke out in favor of the U.S.-Iraq security agreement, saying Iraq's forces still needed the support of the U.S.-led coalition.

"Our forces and capabilities haven't reached the level of self-sufficiency," Zebari said at a joint news conference with visiting French Foreign Minister Bernard Kouchner. "We need this strategic security agreement ... for the time being. But this is not open-ended."

At the same time, the U.S. command is facing a dwindling coalition of allied countries that provide combat power in Iraq.

Australia, one of the first countries to commit troops to the Iraq war five years ago, ended its combat mission here Sunday and began sending its 550 combat troops home. A few hundred others will remain to train the Iraqis and protect Australian diplomats, officials said.

Rudd, the new prime minister, has said the Iraq mission had made Australia more of a target for terrorism and had promised to bring home his country's combat soldiers by the middle of this year. "We have to praise the role of the Australian troops in stabilizing the security situation in the province through their checkpoints on the outskirts of the city," said Aziz Kadim Alway, the governor of Dhi Qar province where most of the troops were based.

The Iraqi government already has assumed security responsibilities for the Shiite-dominated province, which includes the volatile city of Nasiriyah. But the Australians had remained there in case the Iraqis needed help in maintaining order.

American troops will temporarily take over those responsibilities, the U.S. command said.

The Australians had "successfully accomplished their mission" and their contributions "assisted in the stabilization and development of Iraq," U.S. military spokesman Col. Bill Buckner said in a statement.

Britain transferred security responsibilities for the main southern province of Basra last year and pulled its 4,000 soldiers back to the Basra airport last year. Britain suspended plans to remove another 1,500 troops after fighting broke out in Basra in March.

The Poles have also announced they will withdraw some of their 900 soldiers from Iraq by the end of October.

Meanwhile, an American soldier was killed Sunday by an armor-piercing roadside bomb in northeastern Baghdad, the military said. No further details were released.

A car bomb exploded Sunday in a parking lot across the street from the Iranian Embassy, killing at least two civilians and wounding five people, including three embassy guards.

Elsewhere in the capital, a senior police official was wounded and a traffic cop was killed when a bomb stuck to the official's car exploded in a busy intersection.

Two civilians also were killed in separate roadside bombs Sunday near Baqouba, northeast of Baghdad. A policeman and a civilian were injured when a roadside bomb targeted a police patrol in Mosul, an official of the provincial operations center said.

The violence was reported by officials who spoke on condition of anonymity because they weren't authorized to release the information.

Two U.S. soldiers were injured when their helicopter crashed Sunday south of Baghdad, the military said. The military said the crash was being investigated but appeared to be due to mechanical failure.

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Associated Press writers Sameer N. Yacoub and Bushra Juhi contributed to this report.