SAN DIEGO (CNS) — San Diego police have launched an internal investigation after a protester’s arrest by undercover detectives in an unmarked van was partially caught on video last week.

Plainclothes detectives arrested the woman and took her away in the unmarked van after a protest march downtown last Thursday night. The video shows one officer yelling at the woman’s companions, “If you follow us, you will get shot. Do you understand me?”

Warning: Coarse language

Nisleit said on Saturday, “Yesterday afternoon, I directed the Internal Affairs unit to open an investigation into the arrest at 1400 Park Blvd. … The investigation is already under way.”

City Council President Georgette Gomez has called for an investigation of the incident.

“I am calling for an immediate and thorough investigation into this incident, and for the officer who threatened to kill unarmed protesters to be placed on leave,” Gomez said Saturday. “It is incredibly disturbing to hear police officers threaten people’s lives.”

San Diego Police Lt. Shawn Takeuchi said Friday that undercover officers watched the woman swing a cardboard sign at a passing motorcycle officer. He said they arrested her and loaded her into the van for safety reasons because of the surrounding crowd.

The woman was booked into jail on suspicion of assault on a peace officer, Takeuchi said.

“The detective felt that was dangerous because the officer had the potential of being knocked off the motorcycle or crashing it,” Takeuchi said.

Police said the officers involved in the arrest have been reassigned to other duties.