Mt. Gox CEO Mark Karpeles Bloomberg MtGox has been subpoenaed by the U.S. Attorney's office in New York, the Wall Street Journal's Christopher M. Matthews reports.

An unnamed source tells him simply that federal prosecutors sent the subpoena this month.

A spokesman for the U.S. Attorney's office in New York decline to comment to BI.

MtGox shut trading operations last night over what it says were "recent news reports and the potential repercussions on MtGox's operations and the market."

Soon after the WSJ broke the story, Reuters reported that Japanese authorities were also looking into the Tokyo-based exchange.

"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 said in a news conference, according to Reuters.

MtGox has effectively been blackballed within the Bitcoin community. Six of the largest Bitcoin firms published a statement last night denouncing Gox's violation of users' trust, and Gox resigned its position on the Bitcoin Foundation this past weekend.

Meanwhile, Fox News Business' Kathryn Glass says she has obtained a chat transcript conducted by a consultant named Jon Fisher with MtGox CEO Mark Karpeles in which Karpeles claims he is still working to save the firm. Karpeles also says a leaked report indicating a massive, ongoing theft at MtGox, was "more or less legit" but that the document itself had not been produced by Gox.

Business Insider has unsuccessfully tried to reach out to Karpeles, although the Mt. Gox CEO did respond to Reuters via email.

"We should have an official announcement ready soon-ish," he wrote, without providing more details or revealing his location. "We are currently at a turning point for the business. I can't tell much more for now as this also involves other parties."

Bitcoin prices were at $556 as of 9:20 p.m. Eastern.