US President Donald Trump on Monday accused protesters in Los Angeles of insurrection and threatened they would be "hit harder" than ever if they disrespect security forces during clashes triggered by anger over immigration raids.

Demonstrators in a small part of the second biggest US city's downtown area  torched cars and looted stores in ugly scenes Sunday that saw law enforcement responding with tear gas and rubber bullets.

Trump posted he had deployed National Guard troops "to deal with the violent, instigated riots" and "if we had not done so, Los Angeles would have been completely obliterated."

"The people are causing the problems are professional agitators and insurrectionists," he told reporters in Washington.

On social media, he said protesters spat at troops and if they continued to do so, "I promise you they will be hit harder than they have ever been hit before. Such disrespect will not be tolerated!"

California Governor Gavin Newsom accused the president of deliberately stoking tensions by using the National Guard, a reserve military force usually controlled by state governors.

"This is exactly what Donald Trump wanted. He flamed the fires," Newsom said, adding California would be suing the federal government over the deployment.

Trump shot back, saying "I would do it" when asked if Newsom should be arrested.

The protests in Los Angeles, home to a large Latino population, were triggered by dozens of arrests of what authorities say are illegal migrants and gang members.

Trump's border czar Tom Homan said Immigration and Customs Enforcement (ICE) was targeting members of cartels in Mexico and Colombia.

Many locals painted a different picture.

They are "people who are here earnestly trying to improve their lives (and) deserve a chance and don't deserve to be treated as criminals," Deborah McCurdy, 64, told AFP at a rally where hundreds gathered on Monday.

'Isolated'

On Monday morning, a heavy police presence stood watch in Downtown LA, where streets were quiet.

Overnight, vandals had set fires and smashed windows, adding to the scenes of damage left after five Waymo self-driving cars were torched. Obscene graffiti was daubed over many surfaces.

Despite isolated and eye-catching acts of violence, officials and local law enforcement stressed the majority of protesters over the weekend had been peaceful.

Schools across Los Angeles were operating normally on Monday, while the rhythms of life in the sprawling city appeared largely unchanged.

Mayor Karen Bass told CNN that in contrast to Trump's rhetoric, "this is isolated to a few streets. This is not citywide civil unrest."

Immigration arrests were designed to stir tensions, she said, while the troop deployment was "a recipe for pandemonium."

The United Nations warned against "further militarization" of the situation, in remarks likely to anger the White House.

After initial confrontations between demonstrators and federal forces on Sunday, local law enforcement took the lead, using what they called "less lethal weapons" to disperse crowds.

Viral footage showed one rubber bullet being fired at an Australian TV reporter, who was hit in the leg on live television.

At least 56 people were arrested over two days and five officers suffered minor injuries, Los Angeles Police Department officials said, while about 60 people were arrested in protests i San Francisco.

The National Guard is frequently used in natural disasters, and occasionally in civil unrest, but almost always with the consent of local authorities.

Trump's deployment of the force — the first over the head of a state governor since 1965 at the height of the civil rights movement — was criticized by Democrats, including Kamala Harris.

The former vice president and Trump's opponent in the 2024 election called it "a dangerous escalation meant to provoke chaos." 

Mexican President Claudia Sheinbaum on Monday condemned the violence, while calling on the United States to respect migrant rights.

Sheinbaum urged Mexicans living in the United States "to act peacefully and not give in to provocations."

by Huw GRIFFITH