The deployment of the Marine Corps -- typically deployed abroad as a rapid strike force -- is highly unusual for domestic crowd-control scenarios inside the United States.

- Why were they called? -

Protests began last week after Immigration and Customs Enforcement (ICE) agents conducted raids in and around Los Angeles.

The gatherings were mostly peaceful but there were also incidents of vandalism and aggression towards ICE agents and local police.

Some demonstrators breached curfews as they rallied by the downtown Federal Building and the nearby Metropolitan Detention Center, a federal prison holding immigrants.

President Donald Trump first took the controversial step of "federalizing" thousands of California National Guard troops -- sending them to the area against the wishes of California Governor Gavin Newsom and Los Angeles Mayor Karen Bass.

Shortly after, on Monday, the Trump administration announced that about 700 active-duty Marines would also be sent to Los Angeles.

- What will they do? -

US Northern Command (NORTHCOM), which has responsibility over US armed forces operating in North America, said the Marines will protect federal personnel and property.

Major General Scott Sherman, who is leading the Los Angeles mission, said two companies of Marines were taking up position at the Wilshire Federal Building.

Sherman said the Marines would "hold off crowds" as needed.

Military members cannot arrest protesters as that is a law enforcement activity.

But NORTHCOM said Marines could "temporarily detain an individual to stop an assault of, to prevent harm to, or to prevent interference with federal personnel performing their duties."

- Could they get more power? -

The Posse Comitatus Act of 1878 prevents the use of US federal troops such as Marines for domestic law enforcement activities.

But that would change if Trump invoked the Insurrection Act, which lets the president deploy federal troops to suppress a violent rebellion on US soil.

It was last used during the Los Angeles riots in 1992 following the acquittal of police officers involved in the beating of motorist Rodney King.

Under the Insurrection Act, federal troops have the power to conduct searches and arrest people suspected of breaking the law.

Trump has notably not ruled out using the act.

"If there's an insurrection, I would certainly invoke it," he said this week. "We'll see."