Shoppers confront federal agents at Ontario Stater Bros. Markets, video shows

ONTARIO, Calif. (KABC) -- People in Ontario were visibly upset after they encountered federal agents at a Stater Bros. Markets location on Monday morning, video shows.

At least a dozen agents with FBI, Homeland Security Investigations, and U.S. Customs and Border Protection were at the scene, some wearing covers on their faces, and others entering the store.

A number of people pointed their cell phone cameras and shouted at the agents to get out.

The Ontario Police Department was also at the scene. The department said officers responded to the possible assault of a federal agent, but they had no other role beyond that.

A witness told Eyewitness News the federal agents detained a man at an adjacent coffee shop while he was carrying a hot drink.

"They got a person. They dropped the coffee -- hot coffee on their face. When they had him, they threw him to the floor, and hot coffee was spilled. And they took him like that. They didn't even give him the First Aid," Jennifer Palacios said.

Federal agents can be heard in the video telling bystanders they were at the market for a targeted enforcement operation.