By Sophie Knight and Takaya Yamaguchi TOKYO (Reuters) – Any regulation of the bitcoin crypto-currency should involve international cooperation to avoid loopholes, Japanese vice finance minister Jiro Aichi said on Thursday. Commenting on the closure this week of Tokyo-based Mt. Gox, once the worlds biggest exchange for the bitcoin virtual currency, Aichi said the ministry would respond to the problems if necessary, after finding out exactly what happened. As for its legal position, a currency (under Japans jurisdiction) would be coins or notes issued by the Bank of Japan. A document circulating on the internet saying that more than 744,000 bitcoins – worth around $423 million at current rates – were missing from Mt. Gox was created by a Tokyo-based consulting firm, said Ryan Selkis, a blogger who initially leaked scans of the document.