Federal officers and National Guard troops fanned out around a mostly empty Los Angeles park in a largely immigrant neighborhood on foot, horseback and military vehicles on Monday for about an hour before abruptly leaving, an operation that local officials said seemed designed to sow fear.

The Department of Homeland Security wouldn’t say whether anyone had been arrested during the brief operation at MacArthur Park. Federal officials did not respond to requests for comment about why the park was targeted or why the raid ended abruptly.

“What I saw in the park today looked like a city under siege, under armed occupation,” said Mayor Karen Bass, who showed up at the park alongside activists.

She said there were children attending a day camp in the park who were quickly ushered inside to avoid seeing the troops. Still, Bass said an 8-year-old boy told her that “he was fearful of ICE.”