The FBI is looking for four "eco-terrorists" who have been linked to a series of historical arson and sabotage attacks in the Western United States -- three of whom may be hiding out in Canada.

The two men and two women are former members of "The Family," the FBI said Wednesday, an alleged group of radical environmentalists that is accused of making attacks on various targets in Oregon, Washington, California, Wyoming and Colorado between 1996 and 2001.

A US$50,000 reward has been offered for information leading to their individual arrests.

The FBI suspects that Family members Josephine Sunshine Overaker, Rebecca Rubin and Justin Franchi Solondz may be staying in Canada.

The fourth, Joseph Mahmoud Dibee, may be in Syria.

Among other crimes, the group was allegedly responsible for the multi-million-dollar arson of a Colorado ski resort in 1998, which still stands as "the largest eco-related arson in history," the FBI said.

At a press conference on Wednesday, Michael Ward, deputy assistant director of the FBI's counterterrorism division, said approximately 20 people belonged to "The Family" over the years and they credited their actions to both the Animal Liberation Front and the Earth Liberation Front.

Ward said the group "was responsible for at least 25 domestic terrorism criminal actions totaling over $48 million in damages." He said the group was dismantled in 2001, but some members have still not been apprehended.

Ward called the group's members "terrorists."

"Regardless of their political or social message, their actions were criminal and violated federal laws," he said.

Dibee, 41, is an American computer software tester who has also been known by the names "Seattle," "Steve," and "God."

He is 6'3", approximately 150 pounds, and has black hair and brown eyes.

Overaker is in her mid- to late-30s and is known under a variety of aliases including "Osha," "Jo," "China," "Josie," and "Mo."

She reportedly speaks Spanish and may seek work as a firefighter, midwife, sheep tender or masseuse.

Overaker is described as 5'3", 130 pounds, with brown hair and brown eyes. She has several tattoos on her right leg, upper arms, ankles and upper back.

Rubin, 35, is believed to be a Canadian Citizen and has been known by the nicknames "Little Missy" and "Kara."

She is described as being between 5'5" and 5'8" in height, and has brown hair and hazel eyes.

Solondz, 29, has worked as a part-time carpenter and is believed to be traveling in Canada, Europe or Asia.

He is between 5'9" and 5'11" in height, and weighs about 150 pounds. He has brown hair and hazel eyes.

The FBI is advising members of the public not to approach the group members, as they are considered armed and dangerous.

Those with information are asked to contact their nearest FBI office, American Embassy or Consulate.

The North American Earth Liberation Front issued a statement Wednesday in reaction to the FBI reward.

"During the last 10 years, the federal government has wasted countless resources on its 'Operation Backfire' campaign aimed at demonizing those who are protecting the planet," said Lisa Nesbitt, a spokeswoman for the group.

"Instead of tracking and prosecuting nonviolent eco-defenders, why isn't the federal government locking up the real ecoterrorists, the CEOs of corporations who are inflicting violence and destruction on the environment every day?"

With files from The Associated Press