SAN DIEGO - Officials suspect radical environmentalists set a fire that swept through an unoccupied five-story apartment complex, causing more than $20 million in damage. A banner reading "If you build it, we will burn it," with the initials "ELF," was found Friday next to the burning building still under construction in the upscale University Town Centre residential neighborhood. No injuries were reported. The initials may correspond to the Earth Liberation Front, a loose-knit group that describes itself as "an international underground organization that uses direct action in the form of economic sabotage to stop the destruction of the natural environment." Members of ELF have claimed responsibility for dozens of fires and other acts since 1997, causing $50 million in damages to luxury homes, ski lodges and sport utility vehicles. There was no immediate claim of responsibility posted on the group's Web site. The group, which only communicates with the press by e-mail, issued a brief and vague statement in response to media inquiries: "The ELF press office has received no communique for the San Diego fire that took place Aug. 1, 2003, and thus cannot answer any questions as to why this location and city was chosen for the latest ELF action," the statement said. "The banner at the site reading `You build it - we burn it - ELF' is a legitimate claim of responsibility by the Earth Liberation Front." San Diego police, the Federal Bureau of Investigation and arson experts were investigating. Capt. Jeff Carle, of the San Diego Fire Department, said three construction workers who were sleeping on the site managed to escape the flames unharmed. "It could have killed someone," said Carle. Several hundred residents of a building next to the construction site were evacuated as heat from the blaze broke windows and melted plastic blinds in their homes. The 206-unit complex was part of a larger project approved by the City Council in late 2000 that included a hotel and offices. University Towne Centre is a rapidly growing area of apartment complexes and office buildings east of San Diego's tony La Jolla section. Carle said if environmentalists were behind the fire, he didn't understand their motivation: More trees would be cut down to rebuild the structure.