Crowds of Iraqis demonstrate in Fallujah after the Americans, who worked for a North Carolina-based Security company, were pulled from their vehicles, shot and then burned beyond recognition. At least one corpse was then dragged through the streets. The remains of two charred corpses were later seen hanging from a nearby bridge.

"It is our understanding that there were four people traveling in two vehicles," said U.S. Army General Mark Kimmitt told reporters in Baghdad. "What they were doing there, I'm not sure of. Like most contractors, they have a responsibility throughout the country."

The four were identified as employees of the security consulting firm Blackwater USA, which has a contract to provide security for the U.S. government in the Fallujah area.

In Washington, Bush administration officials called Wednesday's attacks a horrific attempt to prevent Iraq's democratic process from moving forward, but vowed those attempts will not succeed. Further north, five American soldiers were killed when their armored personnel carrier ran over a roadside bomb.

Nearly 600 American soldiers have been killed in Iraq since the war began a year ago. In recent weeks, anti-American insurgents have been stepping up attacks on civilians, both Iraqis and foreigners, seen to be cooperating with the U.S.-led occupation authority. Wednesday's violence came just two days after a United Nations official warned the on-going unrest risks jeopardizing Iraqi elections, which are supposed to take place by early next year.

Also Wednesday, several thousand Iraqis demonstrated in Baghdad demanding the Shiite newspaper Al-Hawza, closed by U.S. troops Sunday, be allowed to resume publication. Coalition spokesman Gareth Bayley tells VOA U.S. administrator Paul Bremer reluctantly ordered the paper shut for 60 days, accusing it of attempting to instigate attacks on U.S. troops. "This paper is at the margins and it's publishing articles which can lead to actual deaths and harm to people," he said.

But the move has drawn criticism from freedom of the press groups here in the United States, including the Committee to Protect Journalists. "We think that by closing down a newspaper, particularly in the manner in which the CPA [Coalition Provisional Authority] did, sends the wrong signal to Iraqi media," said spokesman Joel Campagna.