Mizuho Bank <8411.T> said that all of its automatic teller machines (ATM) throughout Japan and its Internet transaction system have stopped working on Thursday, after computer glitches disrupted $7.3 billion worth of transactions over the previous two days.

A spokesman for Japan's second-largest bank said the reason for the outage was not known. He said it was unlikely due to this week's power outages in the Tokyo area and eastern Japan or last week's massive earthquake.

The bank said it would hold a briefing at 0400 GMT about the system troubles.

About 570 billion yen worth of transactions have been disrupted in the past two days, the bank said. The system troubles started Monday morning, with consumers unable to conduct transactions such as cash transfers and money orders.

Shares of Mizuho were down 1.5 percent at 135 yen, outperforming a 2 percent fall in the benchmark Nikkei 225 average <.N225>. ($1 = 78.150 Japanese Yen)

(Reporting by Mariko Katsumura; Editing by Nathan Layne)

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