ESCONDIDO, Calif. -- A team of federal arson experts will join Saturday in efforts to determine the cause of a huge fire that leveled a high-density condominium project under construction in a busy North County district.

Thursday's destructive fire in downtown Escondido rapidly incinerated the four wood-framed structures, throwing flames and a heavy column of smoke high into the air as construction workers fled for their lives.

The inferno resulted in no injuries but caused at least $6 million in damage and forced widespread evacuations. Authorities have disclosed no suspected cause.

Personnel from the FBI and U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives were at the scene within hours, helping local agencies begin the task of pinpointing the origin of the four-alarm blaze.

Saturday, the ATF's National Response Team is slated to arrive at the planned site of what was to be the 122-unit D.R. Horton Paramount Condominiums.

The squad specializes in crisis-scene reconstruction, identification of fire or explosion origins, witness interviews and debris analysis. It is composed of four regional components, organized geographically to cover the United States.

The team normally has 13 to 18 members, including veteran special agents who have post-blast and fire origin-and-cause expertise, forensic chemists, explosives enforcement officers, fire-protection engineers, scenting dogs and intelligence, computer forensic and audit support.

Though the ATF investigates large-scale arson cases, authorities have not disclosed any evidence that the midafternoon blaze near the California Center for the Arts, Escondido, was intentionally ignited.

However, militant environmentalists are suspected of setting at least one major construction-site fire in San Diego County.

In 2003, the Earth Liberation Front, a self-described "international underground movement" resisting urban growth through arson, vandalism and other malicious acts, was linked to a blaze that consumed a five-story apartment complex under construction in the University City area. A hand-lettered message scrawled in dirt near that site was a message suggesting arson: "IF YOU BUILD IT -- WE WILL BURN IT -- THE E.L.F.'s ARE MAD."

Click here to look at the buildings that caught on fire.