Failed Bitcoin exchange Mt Gox said it has found 200,000 coins worth $116m in an old "digital wallet", after it collapsed in February admitting it had lost half a billion dollars in a possible theft.

The Tokyo-based digital currency exchange filed for bankruptcy protection in Japan last month, saying it had lost 850,000 coins worth nearly $500m at present prices.

But 200,000 Bitcoins were left in a "wallet" used before June 2011, the company said in a statement on its website . Bitcoin wallets are used for online transactions between currency holders.

The new find would be worth $116m, according to the CoinDesk Bitcoin price index. The discovery has been reported to the court overseeing the case, the statement said.

Mt Gox, which at one time reportedly processed 80% of global Bitcoin transactions, said that the 200,000 Bitcoins - discovered on March 7 - had been moved to an offline wallet.

The company filed for protection under US bankruptcy law earlier this month, 10 days after doing the same in Japan after a huge loss of the digital currency.

Mt Gox's lawyer said 750,000 Bitcoins belonging to customers had gone, along with Mt Gox's own store of the currency, which she said was around 100,000 units.

Japanese officials have said they were closely monitoring Mt Gox's bankruptcy proceedings, as they try to get a handle on how and why the exchange imploded.

The global virtual currency community was shaken by the events at Mt Gox, which froze withdrawals in early February because of what the firm said was a bug in the software underpinning Bitcoin that allowed hackers to pilfer them.

Unlike traditional currencies backed by central banks, Bitcoin is generated by complex chains of interactions among a huge network of computers around the planet.

After trading for cents per Bitcoin for the first two years of its existence, it began a frenzied climb in 2011 that took it to $40 a coin in late 2012 and $1,100 last year, before falling off to the current $580 level.