By Brad Brooks, Jane Ross, Phil Stewart and Idrees Ali

LOS ANGELES/WASHINGTON (Reuters) -The Trump administration on Monday ordered U.S. Marines into Los Angeles and intensified raids on suspected undocumented immigrants, fueling more outrage from street protesters and Democratic leaders who raised concerns over a national crisis.

Some 700 Marines based in Southern California were expected to reach Los Angeles Monday night or Tuesday morning, officials said, as part of a federal strategy to quell street demonstrations opposing the immigration raids, which are a part of a signature effort of President Donald Trump's second term.

Although their mission to protect federal personnel and property is temporary - filling the gaps until a full contingent of 4,000 National Guard troops can reach Los Angeles - the deployment is an extraordinary use of military force in support of a police operation, and it comes over the objection of state and local leaders who did not request help.

Meanwhile, U.S. Homeland Security Secretary Kristi Noem pledged to carry out even more operations to round up suspected immigration violators, extending a crackdown that provoked the protests. Trump officials have branded the protests as lawless and blamed state and local Democrats for permitting upheaval and protecting undocumented immigrants with sanctuary cities.

The military and federal enforcement operations have further polarized America's two major political parties as Trump, a Republican, threatened to arrest California's Democratic governor, Gavin Newsom, for resisting the federal crackdown.

California sued the Trump administration to block deployment of the National Guard and the Marines on Monday, arguing that it violates federal law and state sovereignty.

The top Democrat on the Senate Armed Services Committee, Senator Jack Reed, said he was "gravely troubled" by Trump's deployment of active-duty Marines.

"The president is forcibly overriding the authority of the governor and mayor and using the military as a political weapon. This unprecedented move threatens to turn a tense situation into a national crisis," Reed said.

"Since our nation's founding, the American people have been perfectly clear: we do not want the military conducting law enforcement on U.S. soil," he said.

The announcement that Marines would be deployed was made on the fourth straight day of protests. Late on Monday police began to disperse hundreds of demonstrators who gathered outside a federal detention center in downtown Los Angeles where immigrants have been held. Police said arrests were being made.

National Guard forces had formed a human barricade to keep people out of the building. Then a phalanx of police moved up the street, pushing people from the scene and firing "less lethal" munitions such as gas canisters. Police had used similar tactics since Friday.

RARE USE OF MILITARY

U.S. Marines are known as the first American forces to establish and beachhead in U.S. military interventions, and as the last forces to leave any occupation.

Though military forces have been deployed domestically for major disasters such as Hurricane Katrina and the attacks of September 11, 2001, it is extremely rare for troops to be used domestically during civil disturbances.

Even without invoking the Insurrection Act, Trump can deploy Marines under certain conditions of law or under his authority as commander in chief.

The last time the military was used for direct police action under the Insurrection Act was in 1992, when the California governor at the time asked President George H.W. Bush to help respond to Los Angeles riots over the acquittal of police officers who beat Black motorist Rodney King.

Newsom contends it is his charge as governor to call in the National Guard, labeling Trump's" action as "an unmistakable step toward authoritarianism."

Trump in turn said he supported a suggestion by his border czar Tom Homan that Newsom should be arrested over possible obstruction of his administration's immigration enforcement measures. "I would do it if I were Tom. I think it's great," Trump told reporters.

FOUR DAYS OF PROTESTS

The protests so far have resulted in a few dozen arrests and some property damage.

"What is happening effects every American, everyone who wants to live free, regardless of how long their family has lived here," said Marzita Cerrato, 42, a first-generation immigrant whose parents are from Mexico and Honduras. 

Protests also sprang up in at least nine other U.S. cities on Monday, including New York, Philadelphia and San Francisco, according to local news outlets.

In Austin, Texas, police fired nonlethal munitions and detained several people as they clashed with a crowd of several hundred protesters.

Before the Los Angeles dispersal, several hundred protesters outside a detention center chanted "free them all," flew Mexican and Central American flags, and directed sometimes-vulgar insults toward federal officers.

At dusk, officers had running confrontations with protesters who had scattered into the Little Tokyo section of the city. As people watched from apartment patios above street level, and as tourists huddled inside hotels, a large contingent of LAPD and officers and sheriffs deputies fired several flash bangs that boomed through side streets along with tear gas.

Homeland Security said its Immigration and Customs Enforcement division had arrested 2,000 immigration offenders per day in recent days, far above the 311 daily average in fiscal year 2024 under former President Joe Biden.

"We conducted more operations today than we did the day before and tomorrow we are going to double those efforts again," Noem told Fox News' "Hannity." "The more that they protest and commit acts of violence against law enforcement officers, the harder ICE is going to come after them."

Los Angeles Mayor Karen Bass opposed the clampdown, telling MSNBC, "This is a city of immigrants."

Noem countered that, "They are not a city of immigrants. They're a city of criminals."

(Reporting by Jane Ross, Jorge Garcia, Brad Brooks and Arafat Barbakh in Los Angeles and Idrees Ali and Phil Stewart in Washington;Additional reporting by Sandy Hooper, Joel Angel Juarez, Kanishka Singh, Ismail Shakil, Doina Chiacu, Steve Holland, Nandita Bose, Lizbeth Díaz, Noé Torres, Alexia Garamfalvi and Dietrich Knauth;Writing by Andy Sullivan, James Oliphant and Daniel Trotta; Editing by Mary Milliken, Ross Colvin, Michelle Nichols, Rod Nickel, Leslie Adler and Michael Perry)