Four of the American soldiers killed were in an amphibian vehicle that hit an explosive device on Wednesday, the military said.

Backed by air power, US marines, sailors and soldiers have launched a huge offensive in the Anbar province.

The US says the assault, which entered its seventh day, is designed to root out fighters near the Syrian border.

Baghdad bombs

Fighters struck again in the capital when a car bomber blew himself up next to an Iraqi police patrol in central Baghdad, killing at least four people, police sources said.

The blast echoed across central Baghdad and thick black smoke rose from burning vehicles in what has become a daily scene since Iraq announced a cabinet.

Iraqi police were the target of
several bomb attacks

In a second attack, fighters hurled grenades at a police convoy in western Baghdad, killing one police officer.

In a separate incident, two Iraqis were killed and two street cleaners injured when an explosive device detonated at a crossroad in the Dora area south of Baghdad.

Bombings have killed more than 400 people in violence that has piled pressure on Iraq's new leaders to deliver on promises of stability.

Although the bombings have targeted mostly police and security forces, Iraqi civilians have also suffered heavy losses.

Civilians killed

In Mosul, multinational forces killed eight Iraqis, including five civilians, when US soldiers opened fire at two vehicles approaching their convoy, a US army statement said. 

In the oil refining town of Baiji, a car bomb blast killed five Iraqis on Friday evening, police said.

Two police officers and two civilians were killed in clashes in the town of Samarra on Saturday, police Captain Hashim al-Sulami said. 

Iraqi soldiers are still the target
of frequent attacks

Two Iraqi National Guards were killed and three others injured when a land mine detonated in al-Madain town, 40km south of Baghdad, Iraqi journalist Walid Khalid told Aljazeera.

Iraqi officials hope the country's security forces will improve after two years of US training, and eventually take over security.

But they can hardly defend themselves - thousands have been killed - and US troops still have to conduct major operations against fighters such as the one in Anbar.

The US military estimated 100 fighters were killed in Operation Matador.

Anbar offensive

The Anbar offensive is focused on an area near the Euphrates north and west of the town of al-Qaim, close to the Syrian border, which Iraqi officials say is used by fighters to cross over into Iraq and carry out attacks.

Iraqi officials say Syria allows
fighters to enter Iraq

Damascus denies Iraqi accusations that it allows fighters to enter Iraq from its border.

Marines launched several air strikes on targets on Friday, including a "terrorist" safe house, the military said. A second air raid targeted fighters manning a vehicle checkpoint.

The US military said marines in al-Qaim witnessed clashes between rival groups. That could not be independently confirmed, but officials in Anbar say followers of al-Qaida's leader in Iraq, Abu Musab al-Zarqawi, have been fighting with tribal groups.

Palestinians arrested

Iraqi and US officials say military firepower is not enough to defeat the fighters, stressing that intelligence is vital.

The acting Palestinian ambassador in Baghdad, Dalil Qussus, said he was surprised to see three Palestinians appear on a popular Iraqi television show that features suspects confessing to "terrorist" acts.

The Iraqi commentator said they planned a bombing that killed 12 people in eastern Baghdad on Thursday.

"There is no way under any circumstances that three brothers could commit this criminal act. It is impossible that the three brothers would return home to their apartment and wait for the police to catch them," said Qussus.

One of the three had a bruised eye.

The three brothers live in a section of Baghdad that has been inhabited by Palestinian refugees for decades.