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The head of troubled Bitcoin exchange MtGox has made his first statement since the service went offline.

Mark Karpeles said he was "working very hard with the support of different parties" to address issues with the service, which went offline on Tuesday.

An estimated 744,000 bitcoins - about $350m (£210m) - are believed to have been stolen thanks to a loophole in Tokyo-based MtGox's security.

Japanese authorities are investigating the company.

"I understand that ministries and agencies concerned - financial services, police and the finance ministry - are looking into the matter to learn the full scope of the issue," said Yoshihide Suga, Japan's chief cabinet secretary.

"Once we have full knowledge of what happened, we will take action if necessary."

Separate investigations into MtGox and businesses linked to it are also said to be taking place in the US, Reuters reported.

Mr Karpeles' statement on Wednesday also addressed concerns he had gone into hiding.

"I would like to use this opportunity to reassure everyone that I am still in Japan," the notice read.

MtGox was a service that allowed people to convert virtual currency Bitcoin in US dollars, and vice versa.

On 7 February MtGox halted transfers of the digital currency to external addresses.

The firm said that thieves had been using a flaw in the system to fool the transaction process into sending double the correct number of Bitcoins.

A leaked report - which Mr Karpeles has confirmed is authentic - said the huge theft had made MtGox insolvent.

Supporters of Bitcoin as an alternative currency have said they are working together to "re-establish" trust among users and were "committed to the future of Bitcoin".

They said they "will be coordinating efforts over the coming days to publicly reassure customers and the general public that all funds continue to be held in a safe and secure manner".