U.S. Homeland Security Secretary Kristi Noem appeared to take a step toward circumventing federal laws that bar the military from taking part in domestic law enforcement in a letter she sent to the Department of Defense Sunday as the National Guard was deployed to Los Angeles amid mass protests over immigration raids.

In a letter obtained by The San Francisco Chronicle, Noem wrote to Defense Secretary Pete Hegseth that the Pentagon should direct military forces "to either detain, just as they would at any federal facility guarded by military, lawbreakers under Title 18 until they can be arrested and processed by federal law enforcement, or arrest them."

The Posse Comitatus Act prohibits the military from taking part in domestic law enforcement without the authorization of Congress.

Noem called on the DOD to "support to our law enforcement officers and agents across Immigration and Customs Enforcement (ICE), Customs and Border Protection (CBP), and Federal Protective Services (FPS), as they defend against invasive, violent, insurrectionist mobs that seek to protect invaders and military aged males belonging to identified foreign terrorist organizations, and who seek to prevent the deportation of criminal aliens."

Noem did not specify the so-called "identified foreign terrorist organizations" that she claimed are involved in the protests that have erupted in Los Angeles in recent days in response to raids by Immigration and Customs Enforcement (ICE), in which 118 immigrants were arrested last week.

President Donald Trump has referred to the protests against his mass deportation operation as "riots," and has claimed those attending the demonstrations are "insurrectionists," but the protests were reported to be "largely peaceful" before Trump ordered more than 2,000 members of the California National Guard to Los Angeles on Saturday.

On Monday, 700 Marines were also deployed.

Syracuse University law professor William Banks told the Chronicle that Noem's request for members of the military to arrest protesters whom she labeled "lawbreakers" could be a step toward "the invocation of the Insurrection Act."

The Insurrection Act was last invoked in 1992 when Los Angeles residents erupted in fury over the acquittal of four Los Angeles Police Department officers who had been filmed savagely beating Rodney King, a black man who they had pulled over after a high-speed chase.

The 1792 law authorizes the president to deploy military forces domestically to suppress rebellions or unrest, when local or state law enforcement is unable to control the situation.

But Stephen Dycus, a professor emeritus at Vermont Law and Graduate School and an expert in national security law, emphasized that local authorities did not appear to lose control of the protests over the weekend.

Noem's requests for military arrests, along with Trump's federalization of the National Guard and deployment of the Marines, "can be seen as using the military, or at a minimum using that threat, to instill fear in the American people and discourage the kinds of protests that are going on in Los Angeles," Dycus told the Chronicle. "So this could be viewed as a preparation for invoking the Insurrection Act, or it could be viewed as part of a larger effort to frighten people who otherwise would exercise their First Amendment guarantee of free speech and protest."

Banks called Noem's push for military detentions of Los Angeles residents "a grave escalation."

The secretary indicated in her letter to Hegseth that she would send a formal request in the coming days. She also called for "the transportation of munitions" from Fort Benning and Wyoming, but did not say what the weapons would be used for.

California state Sen. Scott Wiener (D-11) said Trump's use of the military to suppress protests—which began when ICE agents searched the garment district of Los Angeles for undocumented workers—proves his mass deportation campaign "has nothing to do with deporting criminals and everything to do with creating a militarized terror police state."

"This isn't what happens in a democracy," Wiener told the Chronicle, "this is what happens in a dictatorship."