Authorities monitoring online threats following FBI's Mar-a-Lago raid

Law enforcement agencies around the country are actively monitoring online threats and rhetoric that has emerged in the wake of the FBI raid on former President Donald Trump's Mar-a-Lago estate Monday, sources tell ABC News.

Agencies are also preparing for possible acts of violence they fear could occur at or near pro-Trump demonstrations that some supporters are calling for, law enforcement sources said.

Authorities on Monday morning searched Trump's Florida estate in what sources told ABC News was part of a probe into documents that Trump allegedly improperly took to Mar-a-Lago when he departed the White House, some of which the National Archives has said were marked classified.

"Over the last several months, law enforcement officials across the nation have become increasingly concerned about calls for violence against law enforcement and other government officials by violent extremists," said John Cohen, a former Department of Homeland Security official who is now an ABC News contributor. "The search warrant at Mar-a-Lago has only served to increase those calls, adding to law enforcement concerns."

In the aftermath of the raid, Trump supporters called for protests at FBI offices in Riverside, California, and Washington, D.C., according to online messages collected by the Institute for Strategic Dialogue, a think tank that monitors extremism and hate speech.

The ISD reported that one Trump supporter was "calling on fellow veterans and Americans of all walks to join him" in Washington "to protest the out-of-control FBI and its actions against President Trump," while a post by another supporter implored followers to "Protest FBI tyranny."

Cohen says authorities have grown even more concerned as public figures have echoed those kind of remarks.

"We now face a situation where public officials and members of the media are mimicking the language used by violent extremists, and this has served to add more volatility to the situation," he said.

Evan worse, said Cohen, "there's been talk about a range of conspiracy theories regarding what the FBI was doing at Mar-a-Lago. And when public figures -- especially those who have previously served in law enforcement -- spread wild conspiracy theories that they know are false, it's not only irresponsible but dangerous."

On the other hand, Cohen said, authorities have become better at monitoring threats and acting on them.

"Following the events at the Capitol on Jan. 6, law enforcement has improved its ability to analyze online activities by violent extremists, taking threats made online more seriously and incorporating that understanding into their security planning," he said.