A crowd of immigrant rights advocates blocked a Homeland Security van late Thursday from accessing the Metropolitan Detention Center in downtown Los Angeles.
Video footage showed dozens of people standing in the street, in front of a marked van, chanting, "Drive out ICE!" and "Stop the deportations!" Some held signs.
The protest was in response to raids this week that led to the detention of more than 100 people suspected of violating immigration laws.
The event was organized by the Koreatown Popular Assembly and publicized by Clergy and Laity United for Economic Justice and other groups.
Activists believe Southern California was a target in the sweep in retaliation for so-called sanctuary laws around the region.
"The original goal was to really loudly proclaim that we're not going to stand for ICE destroying families … on Valentine's Day of all days," said Rabbi Aryeh Cohen, who is on the board of an organizing group.
"When the ICE/DHS van came, our group of people decided it was time to put their bodies in front of the machinery of deportation," he said.
Cohen said two agents stayed in the van during the protest. It's unclear whether anyone was detained inside the van.
Los Angeles police officers were called to the protest shortly after 7 p.m., said Officer Tony Im, a spokesman for the department.
"We have a group of protesters that are not allowing ICE agents to enter in or out of the federal building," Im said. "We're currently out at scene addressing the issues."
Activists said police issued a dispersal order about 9 p.m. No one was arrested.
Immigration authorities said this week their enforcement operation began Sunday and focuses on "individuals who pose a threat to national security, public safety and border security."
"This means that, ideally, we are working with local police and county jails to identify public safety threats in their custody, who are also in the country illegally, for deportation," said Immigration and Customs Enforcement spokeswoman Sarah Rodriguez.
But "uncooperative jurisdictions" such as Los Angeles, she added, have forced ICE agents to "conduct at-large arrests in the community, putting officers, the general public and the aliens at greater risk, and increasing the incidence of collateral arrests."
11 p.m.: This article was updated with information about the organizers.