The 75-year-old Chun has been a friend of the former president's since college and is known to have been one of Lee's closest aides throughout his presidential campaign.

Choi, 81, has been dubbed Lee's "mentor." He was tapped to head the KCC in 2008 and retained his post for most of Lee's presidency.

The raids come as part of a widening probe into a string of corruption allegations against the former president, who ruled from 2009-2013.

It is widely expected the prosecution will summon him soon for questioning over the allegations.

A fresh allegation was raised late last month 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.

The former president also faces suspicions that he is the hidden owner of a lucrative local auto parts maker, DAS, which on paper belongs to his eldest brother, and exerted behind-the-scenes influence over management.

He is also implicated in 1.75 billion-won bribery allegations linked to the state spy agency, among other series of suspected corruption. (Yonhap)