The marines were wounded on Sunday after a homemade bomb exploded shortly before 7.30am (0430 GMT) as the convoy passed through the town 100km west of Baghdad.
Two Iraqi civilians, one aged 15, were also killed by sniper fire in clashes between US forces and armed fighters in central Ramadi city, an Iraqi journalist told Aljazeera.
Ten others were injured in the clashes.
The journalist said the city was almost paralysed, with the main roads completely deserted.
Ramadi and nearby Falluja are the two main bastions of anti-US fighters in the Sunni province.
Eight marines were killed and a further 10 injured during a security operation in the area on Saturday, the US military said.
In a statement, the marines adjusted an earlier updated casualty count from nine dead and nine wounded, without offering any explanation for the change.
"The total number of marines killed in action decreases to
eight, wounded in action increases to 10," it said.
The deaths occurred when a car bomb detonated next to a lorry south-west of Baghdad, said Major Clark Watson of the 1st Marine Expeditionary Force.
It was the biggest number of American military deaths in a single day since 2 May, when nine US troops were killed in separate mortar attacks and roadside bombings in Baghdad, Ramadi and Kirkuk.
On Sunday, US artillery shelled Falluja and the military said an air strike had destroyed a mortar bunker used by anti-US forces.
Witnesses said the shelling began at about 8.30am (0530 GMT). It was not immediately clear what the gunners were targeting in the latest of near-daily bombardments of the city.
The US said it had bombed an
enemy mortar bunker
The US military said warplanes had bombed an "enemy mortar bunker" in south-eastern Falluja on Saturday afternoon, setting off secondary explosions.
"Several insurgents were observed walking back and forth from the bunker to two pickup trucks at the time of the strike. The strike uncovered a tunnel," it said in a statement.
US marines have said they are getting set for a major offensive to drive anti-US forces from their strongholds in Falluja and Ramadi, another majority Sunni Muslim city west of Baghdad.
Also in Baghdad on Saturday, a car bombing outside the office of the Dubai-based al-Arabiya television network, killed seven people and injured 19, police and hospital officials said.
Three bodies, including one of a woman, were mangled beyond recognition, said al-Arabiya correspondent Najwa Qasim. It could not be determined whether any of those bodies were of al-Arabiya employees.
Seven people were killed and 19
injured in the blast
However, she confirmed that one guard and one administration worker were among the dead.
Al-Arabiya's managing editor, Abd al-Rahman al-Rashid, said seven people remained missing.
A group calling itself the 1920 Brigades claimed responsibility for the attack, blasting al-Arabiya as "Americanised spies speaking in Arabic tongue" in a statement posted on a website. The station is owned by Saudi investors.
"We have threatened them to no avail that they are the mouthpiece of the American occupation in Iraq," the statement said, warning of more attacks against this "treacherous network".
It was impossible to verify the claim's authenticity.
Al-Rashid, an outspoken critic of "militants" and "terror" attacks, said the station will continue to operate from Iraq.
"This is our job and we won't succumb to pressure," he said from Dubai.