Japanese police on Monday arrested a man linked to knives found on the school desk of Emperor Akihito's 12-year-old grandson.

The incident occurred last Friday as Japan was preparing for Akihito's abdication on Tuesday. Prince Hisahito will become second in line to the Chrysanthemum Throne when his uncle, Crown Prince Naruhito, ascends the throne on Wednesday.

Police said they arrested a man in his 50s on suspicion of trespassing after spotting him in videos from security cameras in the neighborhood of Hisahito's Ochanomizu University Junior High School.

Media reports said the man entered the school posing a maintenance worker and placed two knives on the desk. His motive wasn't immediately known.

Japan's royal family has wide public support but has been targeted in attacks in the past.