TOKYO — The Tokyo police said Monday that they were investigating several Japanese men suspected of planning to go to Syria to fight for the jihadist group Islamic State. The police provided few details of the men, whom they described as university students in their 20s who were not actively attending classes.

They said one of the men, identified as a 26-year-old student at a university in Hokkaido, was recruited by the Islamic State via the Internet. The authorities said the men were the first Japanese suspected of wanting to join the Islamic State.

The police offered no additional information. However, the Asahi Shimbun, one of Japan’s biggest newspapers, quoted an unnamed police source as saying that at least one of the men was recruited through a bookstore in Akihabara, a Tokyo neighborhood that is a center of youth culture.

The newspaper said the bookstore posted an advertisement offering unspecified work in Syria, and telling anyone interested to contact the store. The report said that the 26-year-old student might have responded to that advertisement.