A teacher at a prestigious Tokyo junior high school kicked a student as corporal punishment in mid-September and left him with a broken rib, investigative and other sources with the knowledge of the matter said Thursday.

The male teacher in his 30s at the Ochanomizu University Junior High School has been questioned by police on suspicion of assaulting the second-year student after school, and has largely admitted to the allegation, according to the sources.

The school is known for being attended by 13-year-old Prince Hisahito, the son of Crown Prince Fumihito.

The school consulted the police about the incident in late September and held an emergency meeting for parents to explain what happened, the sources said, adding the boy has already recovered from his injury.

"It is a fact that there was an inappropriate incident, but we cannot give its details as we are consulting the police," said a public relations official at the school.

On April 26, the school had an intruder leave knives on Prince Hisahito's classroom desk. A man arrested three days later over the case voiced criticism of the imperial system and told investigators he had intended to assault the nephew of Emperor Naruhito, who is second in line to the throne. The classroom was empty at the time of his intrusion.