TOKYO—Japanese police questioned a university student and several others Monday over alleged plans to travel to Syria to join the Islamic State group, news reports said.

The reported investigation by Tokyo police would be the first indication of support within Japan for the militant group.

Tokyo Metropolitan Police declined to comment on the reports.

Public broadcaster NHK and Kyodo News service said investigators questioned a 26-year-old male Hokkaido University student and several men who shared a house with him on suspicion they were preparing to go to Syria to fight.

Investigators believe that the student, who is on leave of absence from school, responded to a poster at a used-book store in downtown Tokyo, offering positions for “work in Syria,” Kyodo said. Police have not found records of any travel to Syria.

NHK and Kyodo said police searched the house and the bookstore but did not formally arrest the men.

In Japan, the penalty for someone convicted of preparing and plotting for private combat is up to five years of confinement.

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