The Tokyo-based bitcoin exchange Mt. Gox on Friday filed for bankruptcy protection after a sudden shutdown of all transactions early this week. The exchange's chief Mark Karpeles told a news conference that net current liabilities of Mt. Gox total around 6.5 billion yen ( 63.7 million U.S. dollars) and he apologized for the shutdown that probably impacted at least 1 million users of the exchange. Karpeles said the exchange was hacked in early February and bitcoins may have been stolen, adding the exchange has asked experts to carry forward procedures for filing a criminal complaint, according to Kyodo News agency. Earlier Japanese Finance Minister Taro Aso said he was eager to hold discussions with other ministers and government agencies about the cause of the trouble at Mt. Gox. No existing laws in Japan regulate the virtual currency and government officials said Tokyo will first have to decide which ministry or agency will monitor transactions or illicit activities involving the virtual currency, said Kyodo. Mt. Gox is one of the world's largest bitcoin exchanges. Six other major bitcoin exchanges worldwide have released a joint statement distancing themselves from the troubled operator in Tokyo.