CHICAGO — A police officer has been arrested in the off-duty beating of a 15-year-old high school student, the Chicago Police Department said yesterday.Robert Gallegos, who is charged with aggravated battery, appeared on closed-circuit television yesterday afternoon in a Cook County courtroom, where a judge set bond at $100,000.

The officer, who was assigned to the department’s mass transit unit, was arrested on Saturday, four days after the Juarez High School student suffered a broken jaw and other injuries in the attack, according to a police statement.

Gallegos’ son was involved in a “verbal altercation” with the teen, which allegedly prompted the attack, according to police. Prosecutors told the court that Gallegos approached the teen in an alley, hit him and then threw him against a garage; he also allegedly kicked the boy after he fell to the ground.

A lawyer representing Gallegos at Sunday’s hearing, Jim Thompson, said he disagreed with the prosecution’s version of events, saying the student himself had made threats. As he left the courtroom, Thompson declined to comment to reporters.

Gallegos, who was assigned to the department’s mass transit unit, has been relieved of his police powers, police said. The dispute is the latest in a series of alleged beatings by off-duty Chicago police officers.

Earlier this month, officer Anthony Abbate pleaded not guilty to charges he beat a female bartender and then threatened to arrest bar employees and customers in a failed attempt to suppress a video of the attack.

Three other officers were charged in an another alleged fight with four businessmen at a city bar that authorities say was caught on videotape.