Friday's attack brought the number of dead US soldiers to 118 since Washington declared an end to combat in Iraq on 1 May.
According to Pentagon figures, 114 soldiers were killed in combat during the war in the months of March and April.
Earlier in the day, four civilians and a policeman were killed in clashes at a marketplace in Baghdad's western suburb of Aby Gharib.
The clashes began when US troops tried to clear market stalls from a main road, witnesses said.
Youths began throwing stones at troops and Iraqi police and set tyres ablaze.
"The police tried to contain the protest, the protesters opened fire and a policeman was killed," said police Major Mussa Lazem.
After a three-hour interlude, gunfire erupted again as US armoured vehicles moved into the area and opened fire.
US troops are focusing on finding
According to medic Abbas Jassim three civilians were killed and at least 10 wounded.
In another incident on Friday, two US soldiers were wounded in a grenade attack at the market, according to US army Lieutenant Joseph Harrisson.
Also in Baghdad, two explosions were heard near the US-led occupation forces’ main compound and white smoke was seen above the sealed off security area that includes Saddam Hussein's former presidential palace and other administrative buildings.
A US military spokeswoman at the compound said: "We heard the explosion, but we don't know where it exactly happened."
Attacks outside the capital
In Falluja, a town 65 km west of Baghdad, one resident was shot dead by Iraqi police during the course of an argument.
A strong explosion rocked the centre of the town at midday. Heavy black smoke could be seen billowing from the mayor's office.
Police said following the explosion, residents shouted at the authorities that their neighbourhood had become a target because the US-appointed mayor and other officials worked there.
Two Iraqi civilians were killed by a landmine on a road near a US base north of Baghdad, according to a forensic expert at the Baquba hospital.
"We heard the explosion, but we don't know where it exactly happened"
US military spokeswoman
"The two civilians, who are not older than 30 and are from Baghdad, were heading to Dali Abbas, a hunting area, when the mine exploded," said Hussein Ali, at the hospital, 60 km north of the capital.
He said the road the two were using passes near a US base.
Before dawn, US soldiers sealed off Uja, the village where Saddam Hussein was born, surrounding it with razor wire and setting up checkpoints at the exits. They ordered all adults to register for identity cards in the village about 150 km north of the capital.
Lieutenant Colonel Steve Russell, a battalion commander in the 4th Infantry Division, said he did not know whether Saddam Hussein was directing parts of the resistance, but the village is the family home of many of his former colleagues.
Elsewhere, resistance fighters on Friday mounted a series of harassing attacks on US and Iraqi government targets in the northern city of Mosul, US officers said.
There were no injuries in the overnight shelling of a US base near Mosul, the explosion of a roadside bomb near a US foot patrol on the city's outskirts, or in an attack by fighters who sprayed Mosul's city hall with automatic fire.
Those skirmishes came after a bomb exploded late on Thursday near a military police convoy in northern Baghdad, wounding two US soldiers.