U.S. military troops and federal immigration officers have made a brief but mighty show of force at MacArthur Park in Los Angeles.

Federal officials said it was an immigration enforcement operation, though it was unclear if anyone had been arrested. “It’s the way a city looks before a coup,” Mayor Karen Bass said as she condemned the action.

The Department of Homeland Security wouldn’t say what the purpose of the operation was on Monday, why it ended abruptly, or whether anyone had been arrested.