Fourteen US Marines were killed in western Iraq today when their armoured vehicle was hit by a roadside bomb near the Syrian border.

A civilian interpreter was also killed by the most lethal "improvised explosive device" deployed against US forces since the invasion of March 2003. The attack pushed the number of US military personnel killed in Iraq past 1,800.

The attack happened in the restive al-Anbar province, a tribal region that is at the heart of Iraq's Sunni Muslim insurgency. An estimated 25,000 Marines are stationed in the province.

The Marines killed today were from the same Ohio-based battalion which lost six Marines to an ambush on Monday. An extremist organisation linked to al-Qaeda claimed in an internet posting that some of the Marines, who had been on sniper duty, had their throats slit.

The attack followed the death of an American freelance journalist, Steven Vincent, who had been writing about police death squads operating with impunity under the noses of British troops in the southern city of Basra. Vincent was abducted last night by a group of men in a police car and shot three times in the chest.

His Iraqi translator, to whom he was engaged, was also shot, but survived.

Today's roadside bomb attack occurred just outside Haditha, which is 140 miles northwest of Baghdad in the Euphrates Valley, where American forces are trying to seal a major border infiltration route for foreign fighters.

The American deaths come as the Bush administration is talking about handing more

security responsibility to the Iraqis and drawing down forces next year. At least 39 US soldiers have been killed in Iraq since July 24 - all but two in combat.

The Iraqi Defence Ministry said that since the beginning of April, more than 2,700 Iraqis - about half of them civilians - had been killed in insurgency-related incidents.

The extremist Ansar al-Sunnah Army claimed responsibility for killing the six Marines on Monday. Masked gunmen showed up in the Haditha public market Monday afternoon displaying helmets, flak jackets and other equipment they said were taken from the bodies of the dead Marines.

Fighting has intensified in recent weeks in Haditha, Hit and other dusty towns along the Euphrates River as American forces step up efforts to seal off the approaches to the Syrian border.

The Marines launched a series of operations in the region in May and June in hopes of pacifying the area so that Iraqi military and civilian forces could assume effective control.

But the insurgents have proven resilient.

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