A bomb has killed five US marines near the western Iraqi town of Ramadi, a rebel stronghold where a similar blast killed five marines last week.
Marines patrol out of heavily armed bases across Ramadi
The device went off on Wednesday as the marines' vehicle passed. In a separate attack, a US sailor attached to the marines was shot dead in the town.
More than 1,700 US military personnel have died in Iraq since the invasion in March 2003.
Last Thursday, a bomb killed five marines at Haqlaniya, outside Ramadi.
Ramadi, a town of 400,000 and the capital of Anbar Province, has long been a focus of resistance by Sunni Muslim rebels.
US marines charged with keeping order are said to have found the level of resistance on a par with Falluja, with some districts virtual no-go areas.
The US military releases few details of attacks like that on Wednesday, saying they want to try to protect their soldiers, the BBC's Caroline Hawley reports.
But more than two years after the war started, roadside explosions targeting military vehicles are still the biggest threat to American troops, she adds.
In other violence on Wednesday, militants attacked Iraqi security forces and civilians in and around Baghdad, killing at least 39 people in three separate attacks.
At least 26 Iraqi soldiers were killed in the first blast, caused by a suicide bomber wearing an Iraqi army uniform.
Hours later, a suicide car bomber slammed into a police patrol in the south of the capital, killing eight.
A mortar attack in Baghdad, which appeared to fall short of a police station in the Shurta district, left five civilians dead. Donald Rumsfeld, the US defence secretary, acknowledged this week that Iraq was statistically no safer than it was just after the war.
Since a new elected government was sworn in late in April, well over 1,000 people, most of them Iraqis, have died.