The leader of South Korea's main opposition Democratic Party, Lee Jae-myung, has been indicted on corruption charges.

The Seoul Central District Prosecutors' Office on Wednesday indicted Lee without arrest on five counts, including criminal breach of trust.

The prosecutors say that when Lee served as the mayor of Seongnam, a city south of Seoul, he allowed firms to reap undue profits from a land development project, causing damages of about 490 billion won, or roughly 370 million dollars.

He is also accused of providing favors to companies that made sponsorship payments to a local professional soccer club.

Lee was already indicted in September on charges of making false statements during the presidential election campaign.

Lee said at a party meeting on Wednesday that prosecutors are using their investigation for political purposes. He also said he believes the truth will be eventually revealed in court.

The Democratic Party has been criticizing the administration of President Yoon Suk-yeol over last week's summit between Japan and South Korea. The party said the summit produced no results and that Seoul made concessions to Tokyo.

The main opposition is expected to step up criticism against the government, now that its leader has been indicted.

In the presidential election in March last year, Lee was narrowly defeated by Yoon.