Five US marines have been killed near Ramadi when their vehicle struck a bomb, and in another attack, five Iraqi soldiers have been wounded by a car bomb in Baghdad.

"The five [Iraqi] soldiers have been taken to a Baghdad hospital," an Iraqi Interior Ministry source said, adding that the attack happened at around 8.30am (0430 GMT) on Thursday behind a police station in the northern Sulaikh district.

US military sources, in a statement on Thursday, gave no details of Wednesday's attack but said it was the second time in a week that fighters had inflicted such a high death toll on marines in the same area in a single blast.

US officers have said some rebels have been using "shaped charges", which concentrate blasts onto a small area allowing them to penetrate the heavy armour of tanks.

Improvised explosive devices, as the troops call them, are the biggest threat to Americans in Iraq. Though many are spotted and defused, dozens go off every day.

The US military has strengthened the armour on all its vehicles, at considerable cost in both equipment and in added fuel bills for the heavier loads.

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