American military officials said one soldier died and another was wounded when their convoy came under fire in Tikrit.
Earlier reports said rocket-propelled grenades were fired at occupation soldiers in Tikrit, 175 km north of Baghdad.
In another attack, one US soldier was killed in Mahmudiyah, south of the capital, when his patrol was ambushed.
Eyewitnesses told Aljazeera that rocket-propelled grenades rained down on an American patrol on Ba’quba road, northeast of Baghdad.
US forces, they said, swiftly cordoned off the area and removed any signs of the latest attack in which two military vehicles were destroyed.
A logistics base near Balad, around 75 km north of the capital, was hit by mortar fire, leaving another vehicle badly damaged. A US soldier died in Balad in what American military officials said was a “non-combat” incident.
According to the Pentagon, at least 74 US soldiers have been killed since 1 May when US President George W Bush declared an end to hostilities in Iraq. Among those, at least 29 have been killed in attacks. The US rarely reveal details of “non-combat” incidents.
As the American toll in Iraq rises, Bush admitted on Thursday his government had security problems in Iraq but vowed soldiers would be "tough".
"There is no question we have got a security issue in Iraq," Bush said in Botswana.
Flares lit the skies over Fallujah
In the flashpoint town of Ramadi, there were three separate mortar attacks but there were also no reports of casualties.
In Fallujah, eyewitnesses told our correspondent a huge explosion shook the US headquarters.
American soldiers fired flares in the air before imposing a curfew over the tense city.
On Thursday, Fallujah remained on edge as dozens of former Iraqi police and army officers demonstrated against the continued occupation.
US soldiers pointed their guns at the protesters, who carried banners calling for a handover of power to Iraqis.
Resistance group emerges
A group of Iraqi resistance fighters which is targetting occupation forces, says it has no links or support for Saddam Hussein.
The Iraqi National Islamic Resistance said its armed wing, the '20s Revolution Brigades, vowed to continue resistance attacks until the country was liberated, in a statement obtained by Aljazeera on Thursday.