A 17-year-old boy has been detained after he was accused of sexually assaulting his 12-year-old girlfriend, according to a statement from the authorities of Xintai city, Shandong province, on Monday.

A joint statement released by a team consisting of officers from the local public security, health, and women's federations said the girl met the boy, surnamed Li, via the internet in May, after which they began a romantic relationship which led to a sexual relationship.

Authorities are investigating those responsible for the alleged sexual assault, arranging medical treatment for the girl and providing assistance, psychological counseling and other support, it added.

Previous reports showed that the girl was treated for vaginitis at a local hospital in June and returned in December for treatment of pelvic inflammation, where she also tested positive for Human Papillomavirus (HPV) and had sexual intercourse over the course of six months. However, according to a report in The Paper on Monday, a domestic news portal, the incident was not reported to authorities by any of the hospital staff.

Concerns have been raised regarding allegations that the hospital and implicated doctors may have violated mandatory reporting regulations for cases involving minors. Officials from Xintai city also told The Paper that the investigation would examine whether the hospital failed in its duty to report the case, it added.

Liu Boqian contributed to this story.