Gyeonggi Province Gov. Lee Jae-myung will stand trial for telling falsehoods about a series of allegations raised against him and about his family during his election campaign for the governorship.

The Suwon District Prosecutors' Office indicted Lee without physical detention on charges of violating the national election law, it said.

Lee has been under investigation for allegedly lying about his brother's institutionalization due to a mental illness during his campaign in the runup to the June local elections. 

He denied when he appeared on TV debates as a governor candidate that he had used his authority as the then Seongnam mayor to have his now-deceased brother institutionalized against his will.

The governor also faced accusations after an actress claimed she had an extramarital affair with Lee. Prosecutors decided to not press any charges against Lee, citing insufficient grounds.

"It's what I expected. I'm not baffled," he told reporters following the prosecution announcement.

Lee also hinted that he would not give up his seat over the indictment and will fight the matter in court.

"I still am a proud member of the Democratic Party. I will do my utmost to not cause any more trouble for the party," he said

Prosecutors decided to drop defamation charges against Lee's wife, Kim Hye-kyung, who was under investigation for allegedly posting slanderous messages online about her husband's political rivals, citing a lack of corroboration.

She was suspected of writing the comments using what police have identified as her Twitter ID, "Hyekyunggung Ms. Kim," before and during elections in recent years.

Part of the comments targeted President Moon Jae-in, who battled Lee in the Democratic Party's primary for the 2017 presidential election.

The Twitter ID raised false accusations about Moon's son having landed a job at a public institution because Moon exerted influence while serving as a presidential aide. (Yonhap)