One US soldier has been killed and another injured in an ambush along a road north of Baghdad, the US military has said.
At least 35 US soldiers have died in Iraq since 1 May
Their convoy was hit with a rocket-propelled grenade and small arms fire.
The attack happened at about 0900 (0500 GMT) in a mainly Sunni Muslim area traditionally loyal to ousted Iraqi leader Saddam Hussein.
The soldier's death brought to 153 the number of US troops killed in action since the war began in March - six more than during the 1991 Gulf War.
On Monday, a US soldier and an Iraqi translator were killed in an attack, also within the so-called "Sunni triangle".
The US military says the attacks are carried out by hardliners loyal to Saddam Hussein, who is believed to be in hiding in Iraq and issuing taped messages urging supporters to attack the Americans.
The US has offered a $25m reward for information leading to Saddam Hussein's capture.
The BBC's Paul Wood in Baghdad says roadside bombs or attacks with rocket-propelled grenades are part of the daily reality for US soldiers in Iraq.
He said tactics include using a roadside bomb to take out a Humvee or other vehicle and the fleeing troops are then engaged in small arms fire. The attacker is then able to melt away into the local population.
The tactical awareness and frequency of the attacks means the situation is turning into the nasty, protracted guerrilla war and insurgency campaign that US commanders were always wary of, he says.
US Secretary of State Colin Powell has acknowledged it will take some time to stem the "guerrilla-type" attacks, echoing assessments from US civil administrator Paul Bremer and Defence Secretary Donald Rumsfeld.