US troops have begun a major offensive in the Iraqi city of Fallujah.
The city was sealed off, apparently ahead of the operation to pacify the city, one of the most violent in the heartland of the insurgency against the American occupation.
US commanders have been vowing a massive response after four American security contractors were killed in the city, west of Baghdad, on Wednesday.
The four had their convoy attacked, their vehicles burned. Their charred bodies were dismembered, dragged through the streets and hung from a railway bridge.