The grand jury indicted Eric McDavid, 28, of Foresthill, California, Zachary Jenson, 20, of Washington state, and Lauren Weiner, 20, of Philadelphia, Pennsylvania. The trio was arrested Jan. 13 outside a retail store in Auburn, California, following six months of surveillance of McDavid by federal authorities.

According to Scott, McDavid attended two meetings of anarchist groups, one in July in Indiana and a second in August in Philadelphia, at which he announced intentions to construct explosive devices from common household items.

He also said he planned to blow up several northern California facilities and expressed a desire to kill a police officer, Scott said.

Officials said one of the bombing targets was the US Forest Service Institute of Forest Genetics in Placerville, California. Other potential targets include the Nimbus Dam and Fish Hatchery, east of Sacramento, cell phone towers and electric power stations.

The charges were not related to a separate 65-count indictment handed down on Monday in Washington involving 11 environmental and animal rights activists in the Western United States.

Scott that McDavid recruited the other two defendants and conspired with them to construct homemade bombs and scout potential target locations. He said the trio rented a house east of Sacramento in the foothills where they engaged in bomb-making.

At some point, the three were joined by an unnamed woman who was a government informant.

"Because of the exceptional work of the FBI's Joint Terrorism Task Force and the brave efforts of a confidential source they were prevented from carrying out their planned attacks," the US Attorney said.

"They were acquiring very significant materials. ... We thought it better to shut it down. We were satisfied we had enough evidence to bring a criminal prosecution," Scott said.