SEATTLE  —  Six people were arrested in a string of ecoterrorism attacks in the Pacific Northwest dating to 1998 -- four fires that caused millions in damage and the toppling of an 80-foot power transmission tower, federal prosecutors said Thursday.

The arrests were made Wednesday in Arizona, New York, Oregon and Virginia.

The radical groups Earth Liberation Front and Animal Liberation Front had claimed responsibility for most of the acts.

In the transmission tower attack, bolts were removed from guy wires near Bend, Ore., on the eve of the millennium.

The fires were set at a federal agricultural research facility in Olympia, a logging company's headquarters in Medford, Ore., a lumber company in Glendale, Ore., and a tree farm in Clatskanie, Ore.