The explosion in the Al-Kanat neighbourhood was near the site of an attack on a US convoy which killed five soldiers on Friday.
"According to initial reports, one soldier was killed and three wounded when their vehicle was flipped by an IED (improvised explosive device) blast at around 9:30am (0530 GMT)," said a US military spokesman.
One of the wounded later succumbed to his injuries.
A series of explosions have shaken Baghdad in the past few days, raising fears of more violence ahead of the 30 June transfer of power to the Iraqi interim government by the occupation.
Later in the day three people were killed when the vehicle they were travelling in was ambushed on the main road to Baghdad airport early on Saturday, a US military officer said.
The officer told reporters on the scene that the three were believed to be security contractors en route for the huge US military base at the airport.
The vehicle was completely burnt out and its windows smashed.
A foreign worker was killed and three other civilians wounded when armed men raked their two sports-utility vehicles with machine-gun fire on Saturday in the northern city of Mosul, said the US military.
Earlier, at least 16 Iraqis queuing up to apply for jobs in the new army were wounded on Saturday when a rocket hit a recruiting station in Mosul, the second such attack in a month, security officials said.
One Iraqi security guard was also wounded in the rocket-propelled grenade strike, which followed a mortar attack in mid-May which killed four people and wounded at least 15 lining up at the centre.
"Seventeen people were wounded, 16 of them were waiting for jobs in the new army," said a hospital source.
The attacks came as US forces and Shia militia loyal to Muqtada al-Sadr agreed on Friday to withdraw from holy shrines south of Baghdad and turn over security to the Iraqi police in a bid to end two months of fighting.
Previous US truces with al-Sadr
militiamen have failed to hold
About 50 Iraqi police moved into the area near the Imam Ali shrine late on Friday, but al-Sadr's fighters refused to pull back immediately without firm guarantees that US troops would not hunt them down.
The Americans have refused to negotiate directly with al-Sadr and said they agreed to a request by the governor of Najaf to reposition forces in the interest of peace.
The agreement, if it holds, would be a major step towards ending a two-month Shia uprising. However, the deal only applies to the twin cities of Najaf and Kufa.
As the US military toll rises, so does the threat to suppliers of the occupation forces.
A videotape aired by Aljazeera showed a self-described Kuwaiti truck driver seized by resistance fighters near Baghdad while delivering supplies to the occupation forces.
Earlier a tape obtained by APTN news agency showed the man, who gave his name as Saidan Sadun Saudan Ihreji, saying in Kuwaiti-accented Arabic that he drove a truck from Kuwait under the protection of Iraqi security but was ambushed near the Iraqi capital and taken prisoner.
He said: "I am a truck driver. I loaded my truck with supplies for the Americans to take to Iraq heading to Baghdad. Then I was arrested with the American supplies."
The man advised his "brother truck drivers" not to cooperate with the Americans and added: "And I say before Allah and my mujahidin brothers that I will never come to Iraq again with American supplies."
Several armed, masked men also appeared on the tape, declaring that they were the Al-Waqas Islamic Battalion.
Informer's brother killed
Meanwhile, armed men killed the brother of a man widely regarded as having revealed the location of Saddam Hussein's sons to US troops, in an attack on his car on Saturday, police said.
Saddam's sons Uday and Qusay were killed in July 2003 when soldiers stormed a villa in Mosul belonging to Nawaf al-Zidan, who is distantly related to Saddam. Locals said Zidan had tipped off US forces that Saddam's sons were staying at his villa.
Salah al-Zidan, brother of Nawaf, was killed and three of his relatives were injured when unknown armed men opened fire at their car, Aljazeera's correspondent in Mosul quoted a police source as saying.