WASHINGTON—The world's largest bitcoin trading exchange appears to have taken a key step to comply with U.S. anti-money-laundering rules and potentially avoid additional run-ins with authorities.

A company listed as Mt. Gox this week registered as a money services business with the Treasury Department's Financial Crimes Enforcement Network, according to FinCen's website. Tokyo-based Mt. Gox, which says it handles about 80% of all trading in the virtual currency, couldn't immediately be reached for comment.

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