New York, New York - Masked and armed federal agents carried out sweeping immigration raids in Los Angeles Friday, while others pounced on people at a New York courthouse as President Donald Trump's mass deportation program escalated further.

From courthouses to hardware store parking lots in two of the most diverse cities in the world, federal agents violently wrestled migrants into handcuffs and unmarked vehicles.

They used extreme tactics, conducting unprecedented raids on at least three areas of Los Angeles to detain dozens of people.

At one sweep less than two miles from Los Angeles City Hall, agents threw flash-bang grenades to disperse angry crowds of people following alongside a convoy of Immigration and Customs Enforcement vehicles as protesters hurled eggs and epithets at the agents, media reported.

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"As a Mayor of a proud city of immigrants, who contribute to our city in so many ways, I am deeply angered by what has taken place," LA Mayor Karen Bass said in a statement. "These tactics sow terror in our communities and disrupt basic principles of safety in our city."

White House Deputy Chief of Staff Stephen Miller, who grew up in LA's Santa Monica, insisted on social media platform X that Bass had "no say in this at all."

"Federal law is supreme and federal law will be enforced."

Service Employees International Union leader David Huerta was briefly detained while documenting one of the raids in Los Angeles, according to reports.

"Hard-working people, and members of our family and our community, are being treated like criminals," Huerta said in a statement after his release.

Homeland Security Investigations spokesperson Yasmeen Pitts O'Keefe told the Los Angeles Times that federal agents were executing search warrants related to the harboring of undocumented people.

Hundreds of protesters gathered in downtown Los Angeles on Friday afternoon to demand the release of detainees, facing a brutal police crackdown.

Across the country, plainclothes agents in New York pounced on two immigrants in the hallway of a courthouse Friday.

AFP saw the officers yell for the men not to move before forcing them to lay face-down on the ground as they were handcuffed and arrested.

It was not immediately clear why the two men were arrested.

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ICE agents have intensified such operations in and around American immigration courts in recent weeks.

The Department of Homeland Security revoked regulations that limited agents' access to protected areas such as courts after Trump returned to office in January.

One of the men arrested in New York was Joaquin Rosario, a 34-year-old Dominican who arrived in the US a year ago, registered as he came in and who had his first immigration hearing Friday, his relative Julian Rosario said.

"He was at ease. He did not think anything was going to happen," the relative said, adding that Rosario was so unworried he had not brought his lawyer with him.

Human rights groups are outraged by such operations, arguing that they sap trust in the courts and make immigrants wary of showing up for appointments as they try to gain US residency.

"They're illegal abductions," said Karen Ortiz, a court employee who was demonstrating Friday against the sudden arrests of migrants.

"We need to sound the alarm and show the public how serious this is and one way we can do that is actually physically putting ourselves between a masked ICE agent and someone they're trying to detain and send away," she told AFP.