The Osaka Prefectural Police department is cracking down on a loosely organized crime ring, known in Japanese as "tokuryū," comprised of anonymous members for allegedly forcing about 130 underage girls into prostitution around the country under harsh conditions.

The group, made up of roughly 70 members, is suspected of recruiting minor girls for prostitution through social media.

The police department's juvenile division has arrested ring leader Yusuke Kimura, 34, and four other members for allegations including violations of the anti-prostitution law, and all of them have been indicted. Kimura allegedly forced a female high school student to engage in prostitution with two men in the city of Kishiwada around mid-June last year.