South Korea's financial watchdog found that since June there have been $7.2 billion "abnormal" foreign exchange transactions, most of which were transferred through cryptocurrency exchanges, Bloomberg reported on Thursday.
The Financial Supervisory Service found an additional $680 million worth of "abnormal" money transfers.
Transfers from Hana Bank, Kookmin Bank, Nonghyup Bank, Shinhan Bank, Woori Bank and seven other banks in the country were investigated and the probe will end by the end of October, the report said.
The majority of the funds were transferred to Hong Kong and 82% of the transfers were in U.S. dollars, the report added.
Last month, South Korea had arrested 16 people for their involvement in illegal foreign exchange transactions worth $2 billion. Bloomberg had previously reported that South Korea was investigating Woori and Shinhan for transferring $3.4 billion worth of funds overseas.
A local outlet also reported on Thursday that authorities had seized 259.8 billion won (US$184.4 million) due to tax arrears.
South Korea is cracking down on illegal crypto activity with the Financial Services Commission also planning to expedite new crypto rules. Thirteen digital assets related proposals are in the pipeline.
After issuing an arrest warrant for Terra co-founder Do Kwon, South Korea has also asked Interpol, the international police organization, to issue a "red notice" for Kwon so that he can be arrested wherever he is found. The arrest warrants for Kwon and five others, all Korean nationals, came after the collapse of the $40 billion Terra ecosystem and the ensuing shockwaves that rattled the crypto markets and lead to a series of bankruptcies.
The Financial Supervisory Service was not immediately available to comment when contacted by CoinDesk.