The release of the detainees, all held without trial, has raised hopes for the fate of Jill Carroll, a US reporter seized in Baghdad on January 7 by insurgents who have threatened to kill her unless US forces released Iraqi women in their custody.
"We have released 419 detainees today including five women," a spokesman for the US detention facilities in Iraq told news agency AFP. Another four women are still held in US-administered prisons.
One of the trucks carrying freed prisoners hit a roadside bomb in the Baghdad neighbourhood of Mansur, but it was only lightly damaged and there were no casualties.
Ms Carroll, 28, is one of the nearly 250 foreigners seized in Iraq since the March 2003 US-led invasion, and one victim in a recent spate of hostage taking.
While Iraqi and US officials have denied that the releases have anything to do with Ms Carroll's case, there is hope the move might help.
"Let me assert that there is no connection between the release and kidnapping of the US reporter. The release was finalised after a review by the Iraqi-US board," the US spokesman said.
"When they were detained we had enough evidence to indicate that they were an imminent threat to the security of Iraq and were detained as per the UN Security Council regulations. But there was no trial for a specific crime."
Other kidnappings
Meanwhile US and Iraqi forces are searching for two German engineers, Rene Braunlich and Thomas Nilzchke, seized at gunpoint on Tuesday by men posing as Iraqi soldiers outside an oil refinery in the northern town of Baiji.
The search comes as a delegation of Kenyan Muslims is preparing to visit Iraq to plead for the release of two Kenyan telecommunications engineers abducted last week in Baghdad.
The fate of four Western peace activists seized in November is also uncertain, as is the status of a Jordanian hostage after a videotape from his captors set a new deadline to kill him.
Fresh violence
In rebel violence Sunni Industry Minister Osama al-Najafi survived a roadside bomb attack but his three bodyguards were killed.
The head of an association of former prisoners was shot dead along with one of his relatives, while a police patrol in Baghdad came under attack, with one policeman killed.
In the northern city of Kirkuk, rebels killed five people in separate attacks.