[Updated at 12:06 p.m. ET] Five men have been arrested on suspicion of trying to use what they thought were explosives to destroy a bridge near Cleveland, Ohio, the FBI said Tuesday morning.

Some of the men on Monday planted what they thought were two remotely activated C-4-based explosive devices - which they allegedly bought from an undercover FBI employee - at the base of a Route 82 bridge that crosses from Brecksville to Sagamore Hills over the Cuyahoga Valley National Park, the FBI said in a news conference Tuesday.

The devices actually were inoperable and posed no threat to the public, and the FBI arrested the men shortly after the devices were planted, authorities said.

Douglas L. Wright, 26; Brandon L. Baxter, 20; and Anthony Hayne, 35, were arrested by the FBI's Joint Terrorism Task Force on Monday evening on charges of conspiracy and attempted use of explosive materials to damage physical property affecting interstate commerce, the FBI said.

Also arrested were Connor C. Stevens, 20; and Joshua S. Stafford, 23. Their charges were pending.

Three of the men are self-proclaimed anarchists, the FBI said in a news release.

"The public was never in danger from explosive devices," the FBI said.

The group initially planned to "topple financial institution signs atop high rise buildings in downtown Cleveland" while co-conspirators used smoke grenades to distract law enforcement, according to the FBI. But the plot evolved into plans for using explosive to destroy bridges or other targets, and the group finally decided on the Brecksville-Northfield High Level Bridge, which carries Route 82 over the national park, the FBI said.

Some of the defendants, after they planted the devices, intended to detonate them from a remote location that they believed was safe and could provide them with an alibi, authorities said at Tuesday's news conference.

The FBI learned of the plots through a confidential source who met Wright at a Cleveland-area protest event in November, according to a criminal complaint filed in U.S. district court. Wright told the source that Wright and a group of anarchists "had been discussing plans involving violence and destruction to physical property ... to send a message to corporations and the United States government," the complaint reads.

“The complaint in this case alleges that the defendants took specific and defined actions to further a terrorist plot,” U.S. Attorney Steven M. Dettelbach said in the news release. “The defendants stand charged based not upon any words or beliefs they might espouse, but based upon their own plans and actions.”