South Korean prosecutors have questioned the leader of the country's main opposition party for his alleged involvement in a bribery scandal during his term as mayor.

Democratic Party leader Lee Jae-myung arrived at a prosecutors' office near Seoul on Tuesday, surrounded by his party's lawmakers and supporters.

Local media reports say Lee is suspected of giving favors to companies that had donated to a local pro soccer club when he was the mayor of Seongnam, a city south of the capital.

Lee said the allegations were fabricated, and that he will stand up to the prosecutors.

Lee ran in the presidential election in March last year but was narrowly defeated by Yoon Suk-yeol.

In September, the opposition leader was indicted for making false statements during the election campaign about his involvement in land development projects while serving as mayor.

The Democratic Party, which has a majority in parliament, accuses President Yoon of trying to remove his political rival, and suppressing the opposition.