Tokyo (CNN) Police in Japan have tightened security around Emperor Akihito's 12-year-old grandson after two knives were found near his school desk.

The knives were discovered on Friday in a classroom at the prestigious Ochanomizu University Junior High School, attended by Prince Hisahito.

The mysterious discovery comes just days before Hisahito's uncle, Crown Prince Naruhito, is due to ascend the throne, following the abdication of Emperor Akihito this Tuesday.

According to reports, Hisahito, who is third in line to the throne, but will become second in line after his uncle's ascension, was in a different part of the school building when the knives were discovered.

The two kitchen knives, which had been taped to either end of a stick and whose blades were reportedly painted pink, were discovered balanced between Hisahito's desk and his neighbor's, Japan's Asahi Shimbun reported . Nothing indicating a motive, or a claim of responsibility was left with the contraption.

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