National Guard troops have begun arriving in Los Angeles on orders from US President Donald Trump, in response to clashes between federal immigration authorities and protesters trying to block deportations.

Members of California’s National Guard were seen on Sunday staging at the federal complex in downtown Los Angeles that includes the Metropolitan Detention Center, one of several sites of confrontations involving hundreds of people in the last two days.

Trump has said he is deploying 2000 California National Guard troops to Los Angeles to quell the protests, which he called “a form of rebellion”.

The move came over the objections of Governor Gavin Newsom, marking the first time in decades that a state’s national guard was activated without a request from its governor, according to the Brennan Center for Justice.

Early on Sunday, the deployment was limited to a small area in downtown Los Angeles, with the rest of the city of four million people largely unaffected.

Their arrival follows two days of relatively small protests that began on Friday in downtown Los Angeles before spreading on Saturday to Paramount, a heavily Latino city south of the city, and neighbouring Compton.

As federal agents staged near a Home Depot in Paramount, demonstrators sought to block Border Patrol vehicles, with some hurling rocks and chunks of cement.

In response, federal agents in riot gear unleashed tear gas, flash-bang explosives and pepper balls.

President Trump derided Governor Newsom in a Truth Social post and went on to say that protestors would no longer be allowed to wear masks.

Hitting back on X, Newsom said that the California National Guard hadn’t even deployed in Los Angeles at the time “this rant was posted”.

Tensions were high after a series of sweeps by immigration authorities the previous day, as the week-long tally of immigrant arrests in the city climbed past 100.

A prominent union leader was arrested while protesting and accused of impeding law enforcement.

On Sunday morning, Homeland Security Secretary Kristi Noem said the National Guard would “keep peace and allow people to be able to protest but also to keep law and order”.

The troops included members of the 79th Infantry Brigade Combat Team, according to a social media post from the Department of Defense that showed dozens of National Guard members with long guns and an armoured vehicle.

In a signal of the administration’s aggressive approach, Defense Secretary Pete Hegseth also threatened to deploy active-duty Marines “if violence continues” in the region.

Newsom, a Democrat, described Trump’s decision to call in the National Guard as a “provocative show of force” that would only escalate tensions, adding that Hegseth’s threat to deploy Marines on US soil was “deranged behaviour”.

Vermont Senator Bernie Sanders said the order by Trump reflected “a president moving this country rapidly into authoritarianism” and “usurping the powers of the United States Congress”.

Several Republicans, meanwhile, have voiced support for the involvement of the National Guard.

Among them was Wisconsin Republican Senator Ron Johnson, who stopped short of backing Hegseth’s threat to send in active-duty military personnel.

“My guess is the National Guard ought to take care of the situation,” Johnson said.

Pope rounds on nationalist politics

Pope Leo has criticised the emergence of nationalist political movements, calling them unfortunate, without naming a specific country or national leader.

Leo, the first Pope from the US, asked during a mass with a crowd of tens of thousands in St Peter’s Square that God would “open borders, break down walls (and) dispel hatred”.

“There is no room for prejudice, for ‘security’ zones separating us from our neighbours, for the exclusionary mindset that, unfortunately, we now see emerging also in political nationalisms,” said the pontiff.

Leo, the former Cardinal Robert Prevost, was elected on May 8 to succeed the late Pope Francis as leader of the 1.4-billion-member church.

Before becoming pontiff, Prevost was not shy about criticising US President Donald Trump, sharing numerous disapproving posts about Trump and Vice President JD Vance on X in recent years.

The Vatican has not confirmed the new Pope’s ownership of the X account, which had the handle @drprevost, and was deactivated after Leo’s election.

Francis, Pope for 12 years, was a sharp critic of Trump.

The late Pope said in January that the president’s plan to deport millions of migrants in the US during his second term was a “disgrace”.

Earlier, Francis said Trump was “not Christian” because of his views on immigration.

“A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian,” Francis said when asked about Trump in 2016.

Leo was celebrating a mass for Pentecost, one of the church’s most important holidays.

—with AAP