Four contractors working for the US army have been killed and their bodies mutilated in the Iraqi city of Falluja.
The bodies were dragged from the car and dismembered
The group were shot and burnt in their cars, before a cheering crowd dismembered the corpses and hung two of them from a bridge.
The US State Department has confirmed all four contractors were US civilians.
Elsewhere, five US soldiers were killed in a bomb attack west of Baghdad, in one of the bloodiest days for coalition forces in Iraq for weeks.
Meanwhile three British soldiers were injured when their vehicle was hit by an explosive device in Basra, about 550 kilometres (340 miles) south-west of Baghdad.
A State Department representative said the US government was appalled by the horrific attacks in Falluja and the senseless loss of life.
Hacked to pieces
Witnesses said the contractors were passing through Falluja in two four-wheel-drive vehicles when gunmen opened fire.
An angry crowd descended on the cars, throwing stones and setting the vehicles ablaze.
The victims' remains were hung from a bridge
The corpses were dragged from the wreckage and television pictures showed one burnt body being kicked and stamped on, while at least two were tied to cars and driven through the city, witnesses said.
Adults and children hacked the bodies to pieces, before lynching two of the charred remains from a bridge spanning the Euphrates River.
"The people of Falluja hanged some of the bodies on the old bridge like slaughtered sheep," said local resident Abdul Aziz Mohammed.
One Iraqi held a sign underneath one of the lynched bodies which read: "Falluja is the cemetery for Americans".
US Central Command spokesman Brig Gen Mark Kimmitt said the victims were contractors working for the coalition, but he did not identify them.
A US passport was apparently filmed beside one of the bodies.
Falluja lies within the so-called Sunni triangle north and west of Baghdad, where support for ousted Iraqi leader Saddam Hussein remains strong.
The BBC's Richard Lister in Baghdad says there are clashes in the area almost every day and at least two US troops and several Iraqi civilians have been killed there in the past week.
Coalition forces have been trying to build up their presence in Falluja, to identify insurgents they believe to be operating there.
About 20km (12 miles) north-west of Falluja, five US servicemen died when their vehicle ran over a bomb in Malahma in al-Anbar province, the US military said.
At least 12 people were also reported injured in a suspected car bomb attack in the town of Baquba, north of Baghdad.
US military officials in Iraq say there are now an average of 26 attacks against coalition troops every day, a figure which has increased over recent months.
The casualty figures are even higher for Iraqis, particularly those who are seen to be working with the US-led authorities.