BAGHDAD, Iraq - Three British soldiers were killed and eight were wounded in a suicide bomb and mortar barrage south of Baghdad just days after they gave up the relative safety of southern Iraq for the more dangerous mission of helping U.S. troops in violence-wracked central Iraq.

Three American troops were killed and five were wounded in the same region Thursday.

The British soldiers were with the Black Watch, an 850-strong unit sent to the area to free up U.S. forces for an assault on the militant stronghold Fallujah. British Prime Minister Tony Blair agreed to the move despite considerable opposition at home, even within his Labour Party.

U.S. troops pounded Fallujah with airstrikes Thursday and early today, softening up militants ahead of the expected assault. The targets included a system of barriers rigged with bombs, a command post, suspected fighting positions and a weapons cache, said Lt. Nathan Braden, of 1st Marine Division.

U.S. and Iraqi officials want to clear insurgents from Fallujah and other Sunni Muslim areas north and west of Baghdad so elections can be held by the end of January. American officials plan to use a mixed American and Iraqi force to storm Fallujah if interim Prime Minister Ayad Allawi gives the go-ahead.

The deaths of the three soldiers brought the number of British troops killed in Iraq to 73.

A civilian Iraqi interpreter was also killed in the attack, the worst single combat loss for Britain since three Royal Military Police were killed in the southern city of Basra in August 2003.

Britain's armed forces minister, Adam Ingram, said in London that the attack was carried out by a suicide bomber in a vehicle and that the British checkpoint also came under mortar fire. U.S. forces helped to provide urgent medical support at the scene, Ingram said.

Scottish Nationalist Party spokesman Angus Robertson said the deaths would have "profound implications" for public opinion in Scotland, where the Black Watch regiment is recruited from.

Two of the three American casualties Thursday were Marines killed in combat operations in Anbar province, which includes Fallujah, the military said today. Four Marines were wounded in the same clashes. No other details were given.

A third American soldier was killed and another wounded when a roadside bomb hit their vehicle in Balad, the military said.

Militants and U.S. forces also clashed briefly in Ramadi, but no U.S. casualties were reported.

In the same city Thursday, an Army unit attached to the Marines discovered a youth center boobytrapped with bombs, with a wire leading to a local mosque.

At another mosque in Ramadi, they also found more than two tons of explosives along with other military devices, including rifles, artillery rounds and mortar rounds.

The deteriorating security situation prompted the humanitarian organization Medecins Sans Frontieres, or Doctors Without Borders, to announce it was closing its operations in Iraq. CARE International withdrew from the country after its national director, Margaret Hassan, was kidnapped last month.