Mark Karpeles, the CEO of embattled bitcoin exchange Mt.Gox, has tried to dampen speculation regarding the company, confirming that he has not left Japan -- where the exchange is based - amid reports that regulators are investigating the exchange.

In an update on Mt.Gox's website - which went offline on Monday evening - Karpeles said he was still working hard with the support of different parties to find a solution to the exchange's recent issues. "I would like to use this opportunity to reassure everyone that I am still in Japan," he said. "Furthermore I would like to kindly ask that people refrain from asking questions to our staff: they have been instructed not to give any response or information."

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Mt.Gox, once the world's biggest bitcoin exchange, abruptly stopped trading on Tuesday and its chief executive said the business was at "a turning point," sparking concerns about the future of the unregulated virtual currency. On Wednesday, Reuters reported that the office of Manhattan U.S. Attorney Preet Bharara was seeking information from businesses dealing in bitcoin, in order to discover how they handled the cyberattacks that hamstrung several exchanges in recent weeks. Subpoenas have been sent to Mt.Gox, as well as other firms that did business with the Tokyo-based company, a source told Reuters. Prosecutors want to know more about the nature of the cyber-attacks on Mt.Gox, and other exchanges. Meanwhile, Japanese authorities are looking into the abrupt closure of Mt.Gox, the top government spokesman said on Wednesday in Tokyo's first official reaction to the turmoil at the company.

Mt.Gox - which once claimed it handled around 80 percent of all global dollar trades for bitcoin - is an online marketplace where people can buy or sell bitcoins using different currencies. However, its customers have been unable to withdraw their bitcoins and convert them into U.S. dollars since the beginning of February. The exchange blamed the problem on a critical loophole — known as "transaction malleability" — in the cryptocurrency that it said leaves all exchanges open to hacking.

(Read more: Mt.Gox: All transactions closed 'for the time being')

"At this stage the relevant financial authorities, the police, the Finance Ministry and others are gathering information on the case," Chief Cabinet Secretary Yoshihide Suga told a regular news conference when asked about Tuesday's shutdown of the Tokyo-based exchange.

(Read more: Mt.Gox CEO says bitcoin exchange at 'turning point')