Koo's departure came a day after South Korea's financial watchdog handed down a six month partial suspension of the brokerage's operations and suspended its chief from his duties for three months over the fat finger error.

The regulatory filing did not provide further details.

Samsung Securities in April accidentally issued 2.8 billion shares to employees - more than 30 times the number of its outstanding shares and theoretically worth some $100 billion - some of which were quickly sold off by workers.

The company was not immediately reachable for comment.

(Additional reporting by Diptendu Lahiri in Bengaluru; Editing by Shailesh Kuber/Keith Weir)

By Ju-min Park