Dozens of U.S. Border Patrol agents showed up Thursday morning in downtown Los Angeles, where Gov. Gavin Newsom and other California political leaders were speaking at an event, and detained at least one person in the latest high-profile immigration enforcement operation in the city.

The armed and masked agents assembled outside a museum where the governor was speaking in what Mayor Karen Bass of Los Angeles called “a provocative act.”

A group of masked U.S. Border Patrol agents showed up in trucks outside of the press conference at the Japanese American National Museum.