Federal Agent Punches Handcuffed Man Multiple Times in the Face, on Video

A Customs and Border Protection agent repeatedly struck a man who was lying on the ground handcuffed ... with the violent incident caught on video.

The brutal beating took place near Evanston, Illinois -- a suburb of Chicago -- Friday ... with the video starting off after an agent had already wrestled a man to the ground and slapped a pair of cuffs on him.

The agent brings his fist down on the detainee's face multiple times in the short clip ... bringing forth a chorus of screams from onlookers.

He then grabs the detainee by the back of the neck and forces his face into the ground ... though he ultimately lets up and just holds the man by the wrists before he and his fellow officer pull him to his feet and take him into custody.

We reached out for comment ... and, a Department of Homeland Security spokesperson confirmed these agents were engaged in operations in Skokie and Evanston, which resulted in the arrest of "five illegal aliens from Mexico, whose criminal histories include criminal trespass and multiple illegal entries into the country."

During the course of the operation, DHS claims agents were being "aggressively tailgated" by a red car -- which allegedly crashed into an officer's vehicle while they attempted to make a U-turn. In the background of the clip, you can see the front of a red car touching the back of a border patrol vehicle.

The DHS spokesperson says a crowd of hostile individuals crowded around the scene and began verbally abusing and even spitting on officers ... which is why officers apparently deployed pepper spray.

Agents arrested three United States citizens because of their "violence against law enforcement" in the incident. The DHS spokesperson says such obstructions have become common in recent days.