Authorities are warning of the "substantial" risk that explosives will be among the "tactics" used during protests before and during the Jan. 20 inauguration of President-elect Joe Biden, piling on to a previous memo urging law enforcement to be prepared for armed demonstrations in all 50 state capitols in the coming days, according to a recent report.

An FBI bulletin obtained by ABC News described how the use of "devices targeting infrastructure" has increased in the past several months, and law enforcement should be prepared for the potential use of explosives going forward, according to the report.

FBI INTERNAL MEMO WARNS OF PLANS FOR ARMED PROTESTS IN ALL 50 STATE CAPITALS AROUND DAY OF BIDEN INAUGURATION

The memo reportedly features images of explosives planted during protests over the past several months. Previous devices have also targeted police and the public, it said.

"The danger posed to law enforcement officers and the general public from the all [s.i.c.] the tactics listed is substantial," the bulletin states, according to ABC. "If a suspicious item is reasonably believed to contain explosives, an IED, or other hazardous material, DO NOT touch, tamper with, or move the item. Only bomb disposal personnel should handle any suspected devices that are located."

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A previous internal FBI memo obtained by Fox News warned of plans for armed protests in all of the state capital cities before, during and after Jan. 20.

The FBI told Fox News at the time that the bureau is "supporting our state, local, and federal law enforcement partners with maintaining public safety in the communities we serve." 

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"Our efforts are focused on identifying, investigating, and disrupting individuals that are inciting violence and engaging in criminal activity," the FBI said in an emailed statement. "As we do in the normal course of business, we are gathering information to identify any potential threats and are sharing that information with our partners. The FBI respects the rights of individuals to peacefully exercise their First Amendment rights." 

The statement added: "Our focus is not on peaceful protesters, but on those threatening their safety and the safety of other citizens with violence and destruction of property."

And, the FBI, the Department of Homeland Security and the National Counterterrorism Center announced in a Joint Intelligence Bulletin released Wednesday that violent extremist activity will likely surge in the United States and pose "the greatest domestic terrorism threat in 2021," according to a memo obtained by Yahoo News.

Fox News’ David Spunt and Brooke Singman contributed to this report.