Their deaths pushed the number of US troops killed in three days to 14, part of a surge in attacks that have also killed about 60 Iraqis.

Eighteen US troops have been killed in Iraq during the past week, raising concerns that armed fighters may again be focussing their sights on American forces in addition to Shia Muslims.

The deaths come as American troops are trying to pave the way for a graceful exit from Iraq by giving more responsibility to the country's security forces.

But with the Iraqis still relatively weak, US troops remain in the firing line, targeted by opponents who have shown increasing abilities to attack when and where they please.

More than 620 people, including 58 US troops, have been killed since 28 April, when fighters launched a bloody campaign after Prime Minister Ibrahim al-Jaafari announced his new Shia-dominated government.

'Civil war'

Meanwhile, in the northern city of Tal Afar, there were reports on Tuesday that anti-US fighters were in control and that Shias and Sunnis were fighting in the streets, a day after two car bombs killed at least 20 people.

Police Captain Ahmed Hashem Taki said Tal Afar was experiencing "civil war". Journalists were blocked from entering the city of 200,000.

"The awareness of the Iraqi people and the links between them will prevent such a [civil] war, God willing"

Abd al-Aziz al-Hakim,
SCIRI leader

The man blamed for instigating many of the anti-US attacks, Abu Musab al-Zarqawi, has been wounded, according to a web statement in the name of his group, al-Qaida in Iraq.

But US officials cautioned they did not know if the posting was authentic, and privately said the information might have been designed to purposely mislead.

The Jordanian-born al-Zarqawi has denounced Iraqi Shias as US collaborators and said killing them, including women and children, was justified.

Al-Zarqawi, who like Osama bin Laden has a $25 million bounty on his head, has claimed responsibility for a relentless wave of bombings, kidnappings and beheadings.

Capture

They include a 28 February bomb attack that killed 125 people in Hilla, south of Baghdad, in the single deadliest attack since Saddam Hussein's fall.

Earlier, US forces announced the capture of two fighters with links to al-Zarqawi: Mohammed Daham Abd Hamadi and Mullah Kamel al-Aswadi.

Al-Zarqawi has said attacks on
Shias were justified

Hamadi's cell claimed responsibility for the kidnappings of Chinese and Turks; al-Aswadi is said to be al-Zarqawi's representative in Samarra, north of Baghdad.

Also on Tuesday, Sunni and Shia clerics and politicians intensified efforts to find a way out of a sectarian crisis that threatens a civil war.

Senior officials representing Iraq's two leading Sunni Muslim organisations met Interior Minister Bayan Jabr.

The Sunni officials recently demanded Jabr's resignation, holding his office responsible for the killings of Sunni clerics and others.

Baghdad havoc

Abdul-Aziz al-Hakim, a prominent Shia politician, said there would be no civil war. "The awareness of the Iraqi people and the links between them will prevent such a war, God willing," al-Hakim said.

Al-Hakim, who leads both the Supreme Council for the Islamic Revolution in Iraq and the governing United Iraqi Alliance, said fighters had been trying to start a civil war between the Shia majority and the Sunni minority since Saddam's ouster.

The Baghdad area has seen an
increasing number of attacks

The attacks, al-Hakim said, were "the last card in order to incite sectarian war". He pointed to three against Shias on Monday, which claimed most of the nearly 50 lives lost on that day alone.

But anti-US fighters continued to cause havoc in Baghdad.

Residents called police about a suspicious-looking car parked opposite the Dijlah Junior High School for Girls in Alwiyah, near eastern Baghdad's Withaq Square, a Christian neighbourhood.

As bomb-disposal experts approached the vehicle, it exploded and killed six bystanders. No students were believed to be among the casualties.

Syrian decision

In a separate development, Syria on Tuesday announced that it had ceased cooperation with the CIA and the US army in the wake of what it described as "unfair" allegations by Washington against Damascus, Aljazeera reported.

Syria's ambassador to Washington Emad Mustafa said: "It seems that the US administration has decided to step up pressure on Syria even though the country has completed the withdrawal of its troops from Lebanon and adopted strict measures to prevent the infiltration of armed men from its territory into Iraq."