A powerful bomb exploded near Baghdad's central Liberation Square Monday morning, killing least 13 people, including five foreign civilian contractors who were involved in a project to rebuild Iraq's electricity network, Iraqi and U.S. officials said. Dozens of other people were injured in the blast, which set off an angry anti-American demonstration.

At least one of the foreigners who were killed was an American, the U.S. military in Baghdad said. A spokesman said the others included two British citizens, a Frenchman and another person of undetermined nationality.

Three of the dead were employees of a wholly-owned subsidiary of General Electric Co. called Granite Services, Inc., and two were security contractors working with them, said Gary Sheffer, a spokesman for General Electric at its corporate headquarters in Connecticut. He said the company was not identifying the security firm or releasing any information on names or nationalities.

General Electric works as a subcontractor in Iraq on major power generation projects, Sheffer said, adding that Granite Services provides technical support for such projects. "We remain committed to the reconstruction of Iraq," he said.

The explosion during the morning rush hour destroyed three four-wheel-drive vehicles in a passing convoy -- the apparent target of the attack -- in which the foreigners were riding. Several other vehicles were also destroyed by the explosion, which wrecked shops and tore the facade off a building, exposing three stories of rooms that were reduced to rubble.

The attack, which some witnesses described as a car bombing, set off an angry mob scene in which Iraqis denounced the United States and jumped up and down on the damaged vehicles.

Iraq's new interim prime minister, Ayad Allawi, blamed "terrorists" for the attack, which he said had killed five foreigners and injured three others. Hospital officials said at least eight Iraqis were also killed.

More than 60 Iraqis were injured, many of them with serious burns and lost limbs, news agencies reported.

Reuters news agency reported that a suicide bomber in a red four-wheel-drive vehicle set off the blast.

"We deplore this terrorist act and vow to bring these criminals to justice as soon as possible," Allawi told reporters in a press conference.

"Today's explosion targeted foreign civilians working in the rebuilding of electricity works," Allawi said.

"The terrorists are trying to prevent the transfer of power and sovereignty on June 30," he said, referring to the date on which the U.S.-led occupation authority is to hand power to the Iraqi interim government.

The explosion brought scenes of passionate anti-occupation fervor -- previously seen in Fallujah to the west and Najaf to the south -- to the symbolic heart of Baghdad, just across the Tigris River from where U.S. authorities live and work behind an elaborate security cordon.

An angry mob swiftly gathered around the charred vehicles to denounce the U.S. occupation and promise death to Americans. Young Iraqi men milled around the wreckage, shouting "Down With America" and "Down With Israel." They said the destroyed four-wheel-drive vehicles were carrying Israeli spies escorted by U.S. security guards.

The youths burned a homemade U.S. flag and jumped up and down on the damaged cars, which lay beside Nation Park at the very center of the Iraqi capital. Within half an hour, they had set fire to what remained of the vehicles and danced down the street shouting anti-U.S. slogans.

U.S. soldiers drove up in Humvees and, pointing their weapons in threatening gestures, shouted obscenities to the excited Iraqis and ordered them to back away from the scene. Few Iraqis could comprehend the vulgarities being thrown at them but all immediately understood the meaning of the brandished weapons.

"This is freedom?" a man shouted. "This place isn't for Iraqis any more."

"Americans set off the bomb," another shouted.

"We will slaughter them," a teenager yelled, drawing his finger across his throat.

After half an hour with their M-16 automatic rifles and heavy Humvee-mounted machine guns pointed at the crowd, the U.S. soldiers formed two lines with their vehicles and drove away, leaving Iraqi police in charge. The crowd almost immediately moved in on the vehicles, then threatened an Iraqi police vehicle. Within a few minutes, the Iraqi police moved back and let the mob have its way, burning the cars and shouting their anger at the U.S. occupation.

Bombs have been going off at the rate of about one a day this month as Iraq moves toward a resumption of formal sovereignty after 14 months under U.S. occupation. But most Iraqis, based on what they have seen, have concluded the handover will be more symbolic than real. The young men who raged around the bombing site Monday, for instance, denounced Iraqi police and U.S. soldiers as members of a single hated group -- atheists.

Judging by their slogans, most were backers of Moqtada Sadr, the young Shiite Muslim cleric who has fought the U.S. occupation with a militia called the Mahdi Army. "Long live Sadr, long live Sadr," they chanted.

Papers found at the scene, marked GE Energy Products -- Europe, described a reconstruction project for electricity transmission junctions.

Lack of electricity in Baghdad and other Iraqi cities has been one of the main complaints against the U.S. occupation, particularly now that summer heat raises the temperature above 100 degrees daily.

Branigin reported from Washington.