U.S. Marines deployed to Los Angeles stopped and detained an American citizen trying to enter a federal building this week, as protests over federal immigration raids in that city (pictured) continue to escalate. Photo by Jim Ruymen/UPI

June 14 (UPI) -- Local police deployed pepper spray and non-lethal munitions late Saturday afternoon in Los Angeles as the "No Kings" protest there began to devolve into a more confrontational event.

Many protesters refused to leave local streets after being warned by local police, who then deployed the gas and non-lethal munitions at about 5 p.m. PDT.

The city still has an 8 p.m. curfew that lasts until 6 a.m., so the protest is scheduled to end when the curfew takes effect.

The California National Guard and Marines remain deployed in Los Angeles to help temper unrest in that city.

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The Marines earlier in the day stopped and detained an American citizen trying to enter a federal building.

The man was trying to enter a Veterans Affairs office inside the Wilshire Federal Building in the city's Sawtelle neighborhood when he was stopped earlier this week by Marines sent to protect the property amid protests over immigration raids.

This marks the first time during the current unrest that military troops have detained a U.S citizen.

The 27-year-old U.S. Army veteran was released after a short time.

"They treated me very fairly," Marcos Leao told the New York Times following the incident, adding headphones at first prohibited him from hearing the Marines giving him verbal commands to stop.

U.S. Northern Command confirmed to The Hill, the Marines "temporarily detained a civilian earlier today" under Title 10 of the United States Code governing detention by the armed forces.

Around 200 Marines moved into Los Angeles on Friday, joining thousands of California National Guard troops to help protect federal assets and agents sent to the city to carry out arrests on behalf of U.S. Immigration and Customs Enforcement.

President Donald Trump sent around 700 Marines to the area Monday, but they have thus far been staged outside the city. Gov. Gavin Newsom, D-Calif., has opposed the move.

On Friday, Sen. Alex Padilla, D-Calif., sent a written letter to Trump, signed by all U.S. Senate Democrats demanding the president remove military troops from Los Angeles.

A U.S. District Court Judge in San Francisco on Thursday ruled the president's National Guard troop deployment was illegal. An appeals court later reversed that decision.

Los Angeles officials on Tuesday instituted a local curfew in parts of the city, following over 100 arrests that day amid protesters clashing with police.

On Saturday, millions of people are expected to take part in at least 1,500 protests across the United States. The "No Kings" demonstrations are scheduled to coincide with a major Flag Day military parade in Washington, D.C. and Trump's 70th birthday.

The movement describes itself as "rejecting authoritarianism, billionaire-first politics, and the militarization of our democracy."