US Marine in Iraq (file photo)

In one of the deadliest attacks against American troops in Iraq in recent months, the U.S. Marine Corps says 10 of its troops were killed and 11 wounded late Thursday in a bomb attack near the western city of Fallujah.

Details about the attack on a group of Marines from Regimental Combat Team Eight of the Second Marine Division on Thursday are still sketchy.  

But a spokesman for the multinational forces in Iraq, U.S. Army Lieutenant Colonel Barry Johnson, says members of the unit were walking on a road, when a very large bomb exploded.

"They were conducting a foot patrol outside of Fallujah in the early evening hours and [the attack] appeared to be set up to produce a large number of casualties by placing a number of artillery shells together," said Mr. Johnson.

Thursday's death toll was the highest one-day death toll since August third, when 14 Marine Reserve troops died after their amphibious assault vehicle hit a roadside bomb near the town of Haditha in western Iraq.

Of the 11 Marines wounded, seven sustained minor injuries and have returned to duty. The day before, two Marines from the same unit were killed by small-arms fire in the city of Fallujah. 

The military says the Marines have been working to secure the city and its surrounding areas ahead of national elections on December 15.

Fallujah, about 50 kilometers west of Baghdad, lies in the restive Sunni-dominated Anbar province and had long been a stronghold for insurgents and foreign fighters opposed to Iraq's democratic political process. 

Roughly 13 months ago, U.S. forces, led by the Marines, mounted a massive offensive to root them out.  Since then, the U.S. military and the Iraqi government have been struggling to rebuild the destroyed city and to prevent insurgents and foreign fighters from returning.

The attack on the U.S. Marines Thursday came as the military launched a counterinsurgency operation in the nearby city of Ramadi, the provincial capital of Anbar.  The military says it is the fifth such operation in the area in recent weeks, aimed at disrupting insurgent activities ahead of the elections.

As part of Iraqi government efforts to tighten security for the elections, the interior ministry says it has banned all non-Iraqi Arabs from entering the country until at least December 17. 

U.S. and Iraqi officials have long blamed foreign Arabs for carrying out most of the suicide bombings against Iraqi civilians and coalition forces in Iraq.

On Thursday, the U.S. military said that suicide bombings fell last month to their lowest level in seven months.

Military officials say they believe the decline is the direct result of a series of U.S. and Iraqi offensives conducted recently against insurgent and foreign fighter strongholds in the Euphrates River Valley area of Anbar province.