Atlanta, Georgia - A Salvadoran journalist who was arrested by local police while covering anti-Donald Trump protests in Atlanta has been held by immigration officers, a media advocacy group has said.

Mario Guevara, who has a significant following for his online videos of immigration raids, was detained for obstructing officers and "improperly entering a roadway" by local police during a weekend "No Kings" rally.

He was ordered to be released without bail by a judge on Monday until Immigration and Customs Enforcement officers flagged him for detention, the Committee to Protect Journalists (CPJ) said.

Such a request often precedes deportation proceedings.

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"We are alarmed to learn that reporter Mario Guevara – who has work authorization in the United States – was transferred to Immigration and Customs Enforcement detention after being arrested... while covering a protest," the CPJ said in a statement.

"Guevara must be released without delay. His ongoing detention signals a frightening erosion of press freedom in the US."

The organization said in a letter to the DeKalb County chief executive that "it is chilling to think that the misdemeanor charges against Guevara could trigger his deportation" – despite his having US work authorization and a path to residency through his son.

The Freedom of the Press Foundation also commented on the situation saying, "There is absolutely no reason to deport a longtime journalist who is authorized to work in the United States. The DeKalb County Sheriff's Office should not have released Mario Guevara to ICE."

Guevara was the subject of a 2019 New York Times mini-documentary, in which he said he was attacked and threatened while working as a reporter in El Salvador, leading to his application for asylum in the US, where he has been living since 2004.

Protests have mounted against Trump's aggressive immigration crackdown. According to organizers of nationwide marches, as many as five million demonstrators turned out over the weekend in opposition to the billionaire Republican.