The leader of the ruling Democratic Party on Wednesday pressured former President Lee Myung-bak to come clean about mounting corruption allegations involving his former aides, as prosecutors accelerated probes into them.

Choo Mi-ae made the remarks after prosecutors arrested two key former aides to Lee Tuesday night and early in the morning on allegations of receiving illicit funds from the National Intelligence Service.

Aside from the NIS funding scandal, the prosecution is also looking into suspicions that DAS, a local auto parts maker, stashed away a slush fund for Lee, who ran the country from 2008-2013. Despite Lee's repeated denials, suspicion has persisted that he is the company's actual owner. 

"Lee should now make a confession with regards to the truth (behind the allegations)... It is emerging that Lee lies at the center of the NIS funding scandal and DAS allegations," Choo said during a meeting with senior party officials.

"Lee should tell the real truth, and the prosecution must promptly and thoroughly verify the truth," she added.

Investigators have recently sped up their probe into the NIS funding scandal, with a focus on whether the former president demanded money from the agency or was aware of the money transfers.

Prosecutors suspect that DAS has kept a secret fund worth 12 billion won ($11.2 million) in a way that could constitute crimes of embezzlement and tax evasion.

Meanwhile, Lee did not appear at his office in Seoul despite a plan to hold a meeting with his secretaries. Observers said that he might be shunning contact with media amid speculation that prosecutors could extend their investigation to him.

Lee's supporters have said the probes targeting his former aides amount to "political retribution" by the incumbent government.(Yonhap)