YOMITAN, Okinawa — Japan’s transport ministry is investigating how a tourist was able to fly from Okinawa to Ishigaki Island last week with a World War II-era hand grenade in his bag.

The Ministry of Land, Infrastructure, Transport and Tourism announced Monday that it was investigating how the grenade was missed during routine X-ray scans at Naha International Airport and whether the incident violated the country’s Civil Aviation Act, which prohibits the transportation of explosive material.

The grenade, believed to date from the 1945 Battle of Okinawa, was found by a 20-year-old college student from Yokohama on Takashiho Beach in Yomitan, near the U.S. Army’s Torii Station, according to police reports.

The student told Japanese authorities that he found the grenade, which was corroded and encrusted with coral and at first appeared to be an old seashell, on March 16. He said he carried the object in a plastic bag in his luggage as he stayed at hotels in Yomitan and Motobu and on a Japan Transocean Airlines flight last Friday from Naha to Ishigaki.

He then carried it in his backpack on a ferry ride to nearby Taketomi Island, a police spokesman said.

"I kind of knew that it was a hand grenade, but I never thought that it would explode because it was wet," the student told the Ryukyu Shimpo on Monday.

Police were alerted to the grenade at 9:27 p.m. Sunday when the owner of a guest house on Taketomi Island reported that the student showed him the device. He placed it in a lot near his inn and covered it with an iron pot.

A bomb disposal squad from the Japan Ground Self-Defense Force confirmed Tuesday that the object is a U.S.-made MK2 hand grenade, according to a spokesman for the JGSDF’s First Combined Brigade in Naha.

The grenade is filled with gunpowder and has a fuse, said Chief Warrant Officer Masaru Kaneko.

"It has the possibility of exploding if heat or a strong shock is applied," he said.

No date has been set for disposal of the grenade. The object is about four inches long and three inches in diameter.

Takashiho Beach is on Okinawa’s central west coast, where American forces landed on April 1, 1945. The JGSDF estimates some 2,500 tons of unexploded bombs and shells that rained down on Okinawa during the 83-day battle remain undiscovered.

The otherwise tranquil and peaceful island of Taketomi, a popular tourist destination some 465 miles southwest of Okinawa, was disturbed by the news, said Seihachi Gima of the town’s disaster prevention office.

"At first, I could not believe what I heard," he said. "But what may be even more surprising was the fact that the student carried it around with him while knowing that it was a hand grenade.

"Just imagining that is pretty horrifying."

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