The FBI is offering a reward of up to $50,000 for information leading to the arrest of four alleged environmental extremists accused of sabotage attacks in five western states - including a 1998 firebombing at a Colorado ski resort that caused $12 million in damage.

The four are believed to be members of a radical environmental group known as `The Family' that is blamed for a series of arson attacks, vandalism and other crimes in Oregon, Washington, California, Wyoming and Colorado from 1996-2001.

The FBI identified the four as Josephine Sunshine Overaker, Joseph Mahmoud Dibee, Justin Franchi Solondz and Rebecca Rubin.

The bureau says they are believed to be living outside the United States.

The FBI said 29-year-old Solondz may be in Canada, Europe or Asia, while the 31-year-old Dibee may be in Syria and 35-year-old Rubin in Canada.

Overaker, whose age is listed as 34 or 37, was born in Canada and may be living there, officials say.