SAN DIEGO (AP) - A sabotage campaign by the nation's most radical environmental group has moved from the countryside to the doorstep of Detroit and other major U.S. cities.

The Earth Liberation Front, a movement that originated in the forests of the Pacific Northwest, has claimed responsibility for a string of arsons in the suburbs of Detroit, Los Angeles, San Diego and Philadelphia in the past 12 months. No one has been charged in any of the attacks.

Fires on March 21 destroyed two homes being built in Washtenaw County's Superior Township, west of Detroit. On June 4, two nearly completed houses in Macomb County's Washington Township, north of Detroit, were set afire.

The attacks in Michigan and elsewhere, which included the costliest act of environmental sabotage in U.S. history, have targeted luxury homes and sport utility vehicles, the suburban status symbols that some environmentalists regard as despoilers of the Earth.

"Their actions used to be aimed at 'out in the country' industries," said Ron Arnold of the Bellevue, Wash.-based Center for the Defense of Free Enterprise, who has written several books criticizing the environmental movement's radical wing. "Now they're moving from a save-the-wilderness focus to an anti-capitalist focus."

This summer, environmentalists in Southern California turned six-figure luxury homes under construction into charred sticks of wood, destroyed an unfinished 206-unit apartment complex and firebombed brand-new Hummers, the mammoth sport-utility vehicles that start at $50,000.

Rod Coronado, a legendary figure in the underground movement who is serving as an ELF spokesman and has drawn scrutiny from the FBI, said the group is being transformed by a new generation of activists.

"When I got involved in the mid-'80s, tree-spiking" - pounding spikes into trees to prevent loggers with chain saws from cutting them down - "was a big deal," said Coronado, 37, who played a part in sinking two whaling ships in Iceland and served time in prison for an arson attack at a Michigan State University animal-research lab. "What that's morphed into is a more urban environmental movement, whereby people are fighting for the last wild places in urban areas."

He said the young activists are "doing the only thing they know to do and that is strike a match and draw a whole lot of attention to their dissatisfaction with protecting the environment."

The ELF is the FBI's No. 1 domestic terrorism priority. The organization has done more than $100 million damage - but caused no deaths - since it split off from the radical environmental group Earth First! and surfaced in the United States five years ago.

The ELF first took aim at urban sprawl in 2000, when it burned luxury homes and condos under construction on New York's Long Island.