Prosecutors in South Korea have reportedly raided the largest cryptocurrency exchange in the country, UPbit.

According to CoinDesk Korea, investigators from the Prosecutors’ Office of the southern district of Seoul, the country’s capital, searched the head office of the exchange in the Gangnam-gu district on May 10–11.

UPbit is suspected of fraud for allegedly selling cryptocurrency to customers that it does not actually hold, according to the report. “We have secured hard disks and accounting books through confiscation. Analysis is expected to take days,” the Prosecutors’ Office stated.

When asked for comment by CoinDesk Korea, an UPbit representative said, “At this time, I can not answer anything about this seizure.”

However, the exchange’s support website confirms the investigation in a note posted today and states that its services are still operational, saying:

“UPbit is currently under investigation by the prosecution, and we are working diligently. UPbit services such as all transactions and withdrawals are operating normally. Your assets are kept securely in your account, so you can rest assured that you can use UPbit services.”

The news comes as authorities in the country have been investigating cryptocurrency exchanges amid regulatory tightening in the country.

In March, prosecutors reportedly raided the offices of three cryptocurrency exchanges on suspicion of siphoning off funds from customers’ accounts. One of the exchanges raided was Coinnest, the fifth largest in Korea at the time. Kim Ikhwan, the firm’s founder, and another executive were taken into custody in early April.

Edits: (08:55 UTC) This article has been edited to clarify the the reason for the raid. (10:22 UTC) Updated to add UPbit website statement.

South Korean flag and BTC image via Shutterstock