Police have launched an investigation of a conservative professor who allegedly called Korean victims of Japan's wartime sexual slavery "prostitutes" during a school lecture, a Seoul prosecution official said Friday.

A civic group filed a complaint with the prosecution Monday against Lew Seok-choon, a sociology professor at Yonsei University in Seoul, on charges including libel, sexual harassment and spreading false information.

"We have assigned Professor Lew's case to the criminal division and directed Seodaemun Police Station to conduct the investigation," an official at the Seoul Western District Prosecutors Office said.

According to a recording of his Sept. 19 lecture, the renowned right-wing scholar said the so-called comfort women are "kind of prostitutes" while denying they were forced by the Japanese government to work in military brothels during World War II.

Explaining women enter sex trade largely of their own volition, he said to a female student who challenged him, "If you are curious, why don't you try?"

He faced fierce criticism after the remarks were reported on Saturday.

Yonsei University suspended one of Lew's classes on Monday and a school committee on human rights and ethics began an inquiry.

Students, alumni, civic groups and political parties called on the professor to apologize to the victims and demanded the university fire him.

He said later he meant to stress the need to confirm historical facts and encourage the student to do research.

On Thursday, a Yonsei alumni association submitted to the school president a statement calling for his dismissal, signed by about 3,270 members.

He also quit the main opposition Liberty Korea Party on the day after the party's ethics committee began disciplinary procedures.

He chaired the party's crucial reform committee in 2017. (Yonhap)