The charred wreckage of an overturned truck lay in the rubble that was once the front of a four-story building where a bomb attack killed seven Americans. A U.S. flag dangled from the roof.

The smell of explosives lingered in the air.

Seventy Americans employed by the Vinnell Corp. (search), a Virginia company with a contract to train Saudi military and civilian officials, lived in the building.

By chance, 50 of the Americans were on a training exercise and away from the complex.

The building was in one of three housing complexes in the Saudi capital that were struck by multiple homicide car bombs Monday night. Attackers shot their way into the compounds and then set off the explosives.

The blasts killed at least 20 people, including the eight Americans, Saudi officials reported Tuesday. Authorities also found nine charred bodies believed to be those of the homicide attackers, a Saudi Interior Ministry official said.

Witnesses reported hearing gunfire moments before one of the cars exploded.

One survivor, John Gardiner from Kinghorn, Scotland, told the British Broadcasting Corp. the blasts were "absolutely terrifying."

"All the doors came in, the external doors, the internal doors, all the windows, and the next think I knew I was lying on my back in shattered glass," he said.

The blasts tore through multistory apartment buildings and single-family houses. The force of the explosions sheared off the facades of five- and four- story buildings. Heaps of rubble and blocks of upended concrete surrounded twisted steel bars and knocked downed palm trees. Burned-out hulks that had been cars were still in their parking spots; upended furniture and debris littered a pool deck.

A somber Secretary of State Colin Powell (search), surrounded by a phalanx of aides and security guards, visited the scene for about 10 minutes before departing for Moscow.

"This was a well-planned terrorist attack," he said. "It certainly has all the fingerprints of an Al Qaeda operation."

The bombed building was in the northeast section of the Saudi capital.

A U.S. Army general, speaking on condition of anonymity, said the truck and a sedan drove up to the gate of the complex at about 11:20 p.m. With a brief burst of gunfire, the men in the two vehicles killed the sentries, then pushed the button that opened the iron gate. The truck drove up to the housing complex and its explosive cargo was detonated.

The U.S. general said it was believed the bombers then fled.

Police vehicles, lights flashing, patrolled the walls of the compounds and kept reporters out. The Al-Hamra compound, which suffered one of the worst attacks, was hidden behind 20-foot walls. Surveillance cameras were posted along the walls.

Most of the homes in such compounds are large, single-family villas. Behind high walls, Westerners can escape Saudi restrictions such as the requirement that women outside the home wear enveloping robes. Residents tend to work as corporate executives, oil industry professionals and teachers.

Two of the complexes hit Monday were named after cities in Spain conquered by the Muslim empire in the 13th century. Al-Hamra is Arabic for Alhambra and Eshbiliya is Seville. The third target is Vinnell.