A 31-year-old man was referred to prosecutors Wednesday for allegedly preparing to travel to Syria to join the Islamic State militant group in 2014 while he was a student at Hokkaido University, Tokyo police and other sources said.

The police also sent investigative papers to prosecutors on four other men in connection with the case — a man in Chiba Prefecture who sought to travel to Syria with the Hokkaido student, a man who put up a recruitment poster for work in Syria at a bookstore in Tokyo, a scholar of Islamic law and a freelance journalist.

The five, whose names have been withheld by the police, are suspected of violating the Penal Code by preparing or plotting to wage war upon a foreign state in a personal capacity — the first such case in Japan. The police have recommended that prosecutors indict the men.