Former Democratic Party of Korea Chairman Song Young-gil speaks to reporters after being denied entry at the Seoul Central District Prosecutors' Office on Tuesday. (Yonhap)

The former leader of the main opposition Democratic Party of Korea, a key suspect in an illicit political funding scandal, claimed that the prosecution is politically persecuting him and President Yoon Suk Yeol's so-called "political enemies."

Song Young-gil said Tuesday that the 60-year-old himself and his successor Rep. Lee Jae-myung, as well as some 700 former officials under the previous Moon Jae-in administration, have been targeted by the prosecution in attempt to steer public support toward the Yoon administration.

"The public sentiment cannot change with investigations orchestrated by the prosecution," Song told reporters, reading out a written statement in front of the Seoul Central District Prosecutors' Office.

"Prosecutors have gone too far by launching an all-out investigation into what had happened two years before," he said, referring to the allegations that his aides had illegally distributed cash envelopes to Democratic Party members ahead of the party's national convention in May 2021. Song was elected chairman by a narrow margin at the convention.

Before making the statement, Song voluntarily appeared at the prosecution's office but his entry was denied. The prosecution has imposed an overseas travel ban on Song as he returned home from France, but said it did not intend to interrogate him immediately.

Song is currently a visiting professor at the ESCP Business School in Paris.

Song criticized prosecutors for raiding a party think tank suspected to be behind the illegal campaign financing scheme and to have destroyed evidence.

"I'm making it clear that I've never embezzled funds from the think tank," Song said. "Book records will show that the think tank has nothing to do (with the scandal)."

His close aides are also being unfairly interrogated, he added.

"I strongly urge the investigators to stop threatening people around me. They had better put me in detention and interrogate me."

He declined to elaborate on other alleged evidence, saying it would be disputed in the courtroom.

Song also called on law enforcement authorities to carry out a prompt investigation into prosecutors, journalists and government officials over leaked audio recordings related to campaign financing allegations, adding that it would lose admissibility. Under the Korean law, an act of revealing facts of a suspected crime is subject to up to three years of imprisonment.

Former Democratic Party of Korea Chairman Song Young-gil walks out of the the Seoul Central District Prosecutors' Office after he was denied entry there on Tuesday. (Yonhap)

The prosecutors see Song as an accomplice in violation of the Political Parties Act and the Political Funds Act.

In April, voice recordings of Democratic Party members alleged that at least 94 million won ($70,100) in cash was distributed to party members through Song's aides without proper bookkeeping.

Illegal fundraising for election campaigns during a party convention is deemed a criminal act in Korea. Those who exchange money or favors may face up to three years or imprisonment or a fine of up to 6 million won, and those who brokered the illegal fundraising are subject to five years of imprisonment or up to a 10 million won fine.

Korea considers any political fundraising beyond the legal cap or without proper record-keeping through authorization of election authorities as illegal.

Chairman Lee extended an apology to the public over the allegations, and urged Song to return to Korea. Prosecutors have conducted search and seizure operations at multiple locations, including Song's residence and the party think tank, since Saturday.

Song stepped down in March 2022 immediately after Lee's narrow loss in the presidential election against Yoon, a former prosecutor. Lee succeeded Song's post in August.