Another allegation raised this week is that Lee Pal-seung, a former chief of Woori Finance Holdings, paid the ex-leader some 2.2 billion won ($2.03 million) in bribes to take the top seat at the then state-controlled major lender.

"For now, we have to conduct an investigation into newly raised suspicions," a prosecution official said. "We can't set a deadline as we conduct the investigation."

Lee, who was in office from 2009-2013, is at the center of a ballooning scandal involving his brother's auto parts manufacturer, DAS. Prosecutors suspect that Lee is the real owner of the company and has used it as a channel to hide assets, among other irregularities.

Former top aides of Lee were also accused of receiving illicit money from the state intelligence agency. Prosecutors suspect the money was channeled to the presidential office at Lee's instruction. While indicting one of Lee's closes aides over the allegations, prosecutors described the aide as an accomplice and Lee as the main culprit.

Some of Lee's family members and key aides have been questioned, and some of them have been arrested.

Lee has rejected all allegations against him, denouncing the investigation as political retaliation by the current liberal government.(Yonhap)