A court on Saturday issued an arrest warrant for a close confidant of Lee Jae-myung, the chairperson of the main opposition Democratic Party, on charges of taking illegal political funds from real estate developers.

The Seoul Central District Court issued the warrant for Kim Yong, deputy head of the DP-affiliated Institute for Democracy think tank, on suspicion of receiving a total of 847 million won ($593,552) from property developers in the city of Seongnam in violation of the political fund law.

He allegedly took the funds between April and August last year ahead of the party's primary election to pick the candidate to run for this year's presidential election. Lee won the party's presidential nomination but was defeated by a narrow margin by President Yoon Suk-yeol in the March election.

Kim served as a high-level aide in charge of fundraising on the primary election campaign for Lee.

The real estate developers in question are key suspects in a corruption case involving a lucrative housing development project in Seongnam's Daejang-dong district that is currently under a prosecution probe. Lee was Seongnam mayor when the project was launched in 2015.

The arrest warrant against Kim is widely interpreted as a sign the probe is closing in on Lee.

Earlier this week, prosecutors apprehended Kim and searched his home in a probe into the allegations. They also attempted to raid his office inside the DP's headquarters only to face intense resistance and protest by party politicians.

On Thursday, Lee strongly denounced the prosecution's attempted raid as "oppression" of the opposition party and claimed Kim's innocence. Lee also flatly denied the allegations, saying he has never used a penny of illegal funds.

Prosecutors are expected to expand the investigation to determine whether any illegal political funds were used in Lee's 2014 run for the Seongnam mayoralty or any other elections. (Yonhap)