US soldiers mistakenly shot dead two Iraqi policemen and two civilians after an attack on their convoy, the Iraqi interior ministry reports.
The US is trying to win hearts and minds among the Sunnis
The incident happened south of Baghdad on Saturday just hours after a US bombing error left at least five dead near the northern city of Mosul.
US forces apologised for bombing the house but no comment was available immediately after the shooting deaths.
A fifth Iraqi died of a heart attack after the shooting, police added.
According to the Iraqi interior ministry, US troops opened fire on Saturday evening after their convoy was hit by a roadside bomb at a checkpoint at Yussifiya, 14km (nine miles) south of the Iraqi capital.
The area is part of the notorious Triangle of Death, where Sunni-led opposition to the US occupation is strong.
With just three weeks to go before elections, the BBC's David Willis notes, US officials have been meeting with leaders of Iraq's Sunni community in an attempt to get them to lift their threatened boycott of the vote.
Sunni leaders maintain Iraq's security situation is now so unstable that holding free and fair elections is virtually impossible.
In other developments:
- A bomb being removed for disposal explodes and kills seven Ukrainian soldiers and one Kazakh in Wasit province
- Gunmen shoot dead the deputy police chief of the city of Samarra, Maj Muhammad Muzaffar
- Iran opposes any postponement of the Iraqi elections which, President Mohammad Khatami says, will facilitate "the exit of occupation forces".
Earlier on Saturday, an American jet dropped a 500-pound bomb on a house near Mosul. The owner put the number of dead at 14, including seven children.
Reporting only five deaths in Aaytha and referring to the loss of "possibly innocent lives", the US military promised an investigation.
"The house was not the intended target for the air strike. The intended target was another location nearby," a statement said.