Brigadier General Mark Kimmitt said the soldier was shot dead in the northern city of Mosul on Monday, which has seen an upsurge in attacks on US troops.
"There was a drive-by shooting by four Iraqis. They shot and killed him," he said.
The shooting brought to 308 the number of US soldiers killed in action in Iraq since they invaded in March, including 193 killed since major combat was declared over on 1 May.
On Sunday, a roadside bomb blast in Mosul killed one US soldier and wounded two. Last month resistance fighters mortared the headquarters of the 101st Airborne, killing one soldier.
Bomb expert killed
Foreign contractors are being
targeted in attacks
And in Baquba, 65 km north of Baghdad, a police bomb disposal expert was killed when a tank round planted on a busy street was detonated by remote control.
Iraqi police and others seen to be working or cooperating with US authorities are increasingly the target of attacks.
Last month 17 policemen were killed in twin bomb blasts in and near Baquba.
While the US military says the overall number of attacks has declined following a recent offensive against resistance fighters, November was still the deadliest month for US troops since Saddam Hussein was overthrown.
Contractors pull out
Earlier on Monday, a group of South Korean electrical workers left Baghdad for Jordan following the killing of two of their colleagues late last month.
More than 40 contractors working for South Korea's Ohmu Electric Co Ltd on a project to rebuild Iraq's power infrastructure have left in the past two days.
And Bangladesh said it had closed its embassy in Baghdad and evacuated its diplomats to neighbouring Jordan after an e-mail threat to blow up the mission.
War crimes tribunals
Meanwhile, in Baghdad, Abd al Aziz al-Hakim, the president of the US-backed Governing Council, said steps were being taken to set up war crimes tribunals to try former senior members of the regime for crimes against humanity.
"These trials can be public, with representation by lawyers... All of this can assure the justice and scrupulousness of the tribunals"
Abd al Aziz al-Hakim on Iraqi war crimes tribunals
"They will be in the hands of Iraqis, with an Iraqi criminal law. It's possible that there could be judges from abroad, the United Nations or other countries, as observers. These trials can be public, with representation by lawyers," he said.
"All of this can assure the justice and scrupulousness of the tribunals," Hakim, a cleric who heads Iraq's largest Shia Muslim political movement in the country, said.
Many of those of who could face trial appear on the US Army's 55 most-wanted list. Most have already been detained, but Saddam remains at large with a $25 million bounty on his head.