Bitcoin plunged to a three-week low Friday after South Korean prosecutors raided the country’s largest cryptocurrency exchange over fraud concerns. The raid came just before the start of the showpiece Blockchain Week New York event, which usually serves as a tailwind for the speculative asset class.

Bitcoin fell 5.5% to $8,511.70, the lowest level since April 20, before ticking up to $8,634.59, according to Coindesk. Other digital currencies were also hit, with Ethereum down 5.7%, Bitcoin Cash 6% and Ripple, also known as XRP, 7.6%.

Among Bitcoin-related stocks, Riot Blockchain (RIOT) was up 2.4% on the stock market today, Overstock.com (OSTK) was up 2.2%, Marathon Patent Group (MARA) fell 2.7%and Bitcoin Investment Trust (GBTC) lost 3.8%. The movement came after it emerged that investigators from the Prosecutors’ Office in the capital of Seoul raided the head office of the UPbit exchange on May 10-11, according to CoinDesk Korea.

Korea’s largest cryptocurrency exchange is suspected of committing fraud by selling coins to customers it does not actually hold. Hard disks and accounting books were confiscated for analysis.

“UPbit is currently under investigation by the prosecution, and we are working diligently,” a statement on the firm’s website said. “UPbit services such as all transactions and withdrawals are operating normally. Read more from investors.com…

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