TOKYO—Japan's chief government spokesman and a member of the central bank's policy board said authorities were looking into the regulation of bitcoin, a day after Tokyo-based bitcoin exchange Mt. Gox shut its website and halted trading.

Compared with regulators in many other advanced economies, Japanese regulators have been relatively silent on bitcoin. But Wednesday, after Mt. Gox's abrupt closure underscored the risks of a virtual currency, several of them started speaking.

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