A pedestrian walks past the by KB Kookmin Bank's headquarters in Seoul, Thursday. Yonhap

Just as KB Financial Group’s race to choose its next chairman enters a decisive stage, tax authorities have launched a unscheduled investigation into its flagship unit, KB Kookmin Bank — a move that could add an unexpected complication to the succession process, according to industry experts, Friday.

The National Tax Service (NTS) dispatched around 30 officials from its high-profile investigation bureau 4 to the bank’s Seoul headquarters, Thursday, to secure accounting records after reportedly detecting possible signs of tax evasion. The investigation is expected to run through the end of the year.

Known in corporate circles as the NTS’ “grim reaper,” bureau 4 is an elite unit that handles major investigations into large companies and high-income individuals suspected of serious tax offenses. Its probes are relatively rare and can result in hefty tax bills, penalties or criminal charges.

KB Financial Group Chairman Yang Jong-hee / Courtesy of KB Financial Group