BEIJING -- Peking University is to continue to tighten rules on staff conduct and discipline teachers who fail to live up to standards.

The university took its strong stance in response to mounting calls for the school to investigate an alleged sex scandal involving a former teacher, some 20 years ago.

Shen Yang, a Chinese language professor, is accused of having sexually assaulted a female student who committed suicide in 1998. The matter resurfaced this week after a person who claims to be the victim's former classmate published the allegations online and, demanding a thorough investigation.

Shen, who has left Peking University in 2011 and now teaches in another school, denies the accusation, according to a local media report.

Peking University, however, said in a statement that police investigated the case in 1998 and the school gave Shen an administrative punishment.

The statement did not elaborate on the investigation result or the punishment.

Peking University said it has raised standards of teacher behavior and has been strict and consistent in dealing with teacher behavior.

"In recent years, some teachers were found to have problems. Every case has been thoroughly investigated and offenders have received grave penalties," the school said.