More than a dozen expensive homes under construction were burned down early Monday in a suburban Washington (search) housing development that had been criticized by environmentalists because it is next to a nature preserve, officials said.

An FBI (search) agent said the fires may have been set by environmental extremists.

A dozen homes were destroyed and 29 others damaged near the state's Mattawoman Natural Environment Area. No injuries were reported. The damage was estimated at least $10 million.

There was no immediate claim of responsibility.

Faron Taylor, a deputy state fire marshal, said investigators believe fires were set in at least four of the homes, which were priced at $400,000 to $500,000. Taylor refused to say what led investigators to conclude it was arson.

"At this point, our knowledge of the methodology is shared by us and the perpetrator, and we don't want to share that with anyone else," Taylor said. "We're not going to tip our hand."

A Sierra Club (search) report had called the development "quintessential sprawl" because it is far from existing infrastructure and "threatens a fragile wetland and important historical sites near the Chesapeake Bay."

After the fires, the Sierra Club issued a statement saying it "strongly condemns all acts of violence in the name of the environment."

FBI spokesman Barry Maddox said agents were on the scene and would investigate whether the fires were an act of ecoterrorism.

"Anything and everything will be considered, but we're not labeling this anything other than suspicious fires," Maddox said.

The blazes were reported before 5 a.m., drawing firefighters from four counties to the subdivision about 25 miles south of the nation's capital. The houses, on lots of about a quarter-acre each, were spread across a 10-acre area, Taylor said.

"This was a very, very affluent neighborhood under construction," Taylor said.

Taylor said the fire would be investigated by agents from the Maryland fire marshal's office and the federal Alcohol, Tobacco, Firearms and Explosives, which is routinely brought in to help investigate large fires.