FALLUJAH, Iraq - In one of the bloodiest days in weeks for the U.S. military, five troops died when a bomb exploded under their military vehicle west of Baghdad on today. At least four foreign nationals, including one American, were killed in a separate attack and some of the bodies were burned, beaten and hanged from a bridge.

The explosive device that killed the American troops blew up when their vehicle ran over it, U.S. Army Col. Jill Morgenthaler said in Baghdad. The attack happened in Anbar province, which encompasses Fallujah, Ramadi and other towns where anti-U.S. insurgents are active.

Residents said the bomb attack occurred in Malahma, 12 miles northwest of Fallujah. U.S. Marines operate in the area, but it was unclear whether the slain troops were Marines.

In another attack today, gunmen in Fallujah attacked two four-wheel-drive civilian vehicles, killing their occupants and setting the cars on fire. Some witnesses said four people were in the vehicles, others said six.

Footage from Associated Press Television News showed one man beating a corpse with a metal pole. Others tied a cord to one of the bodies, attached it to a car and drove it down a street, surrounded by a cheering crowd. An Associated Press reporter saw two blackened bodies hanging from a bridge.

"The people of Fallujah hanged some of the bodies on the old bridge like slaughtered sheep," resident Abdul Aziz Mohammed said. Some of the corpses were dismembered, he said.

APTN footage showed the charred bodies of three slain men. Some were wearing flak jackets, said resident Safa Mohammedi.

One resident displayed what appeared to be dog tags taken from one body. Residents also said there were weapons in the targeted cars. APTN footage showed one American passport near a body and a U.S. Department of Defense identification card belonging to another man.

Witnesses said the two vehicles were attacked with small arms fire and rocket propelled grenades.

Hours after the attack, the city was quiet. There were no U.S. troops or Iraqi police in the area.

Fallujah is in the Sunni Triangle, where support for Saddam Hussein was strong and rebels often carry out attacks against American forces.

In nearby Ramadi, insurgents threw a grenade at a government building and Iraqi security forces returned fire today, witnesses said. It was not clear if there were casualties.

Also in Ramadi, a roadside bomb exploded near a U.S. convoy, witnesses said. U.S. officials in Baghdad could not confirm the attack.

On Tuesday in Ramadi, one U.S. soldier was killed and another wounded in a roadside bombing, said Brig. Gen. Mark Kimmitt.

The attacked convoy is normally used to transport the Diala provincial governor, Abdullah al-Joubori, but he was elsewhere at the time.

The latest violence came two days after Carina Perelli, the head of a U.N. electoral team, said better security is vital if Iraq wants to hold elections by a Jan. 31 deadline. The polls are scheduled to follow a June 30 transfer of sovereignty.

Top U.S. administrator L. Paul Bremer said Tuesday he had appointed 21 anti-corruption inspectors general to government departments to try to prevent fraud.