When the subprime crisis ran riot and U.S. and European central banks launched a series of coordinated assaults earlier this year, Bank of Japan Gov. Masaaki Shirakawa stood aside and merely released statements hailing his peers' efforts.

Thursday, however, the BOJ announced it would take a role in an alliance of central banks, joining the battle against a drying out of liquidity in money markets — a move underlining the increased seriousness of the crisis.

"Growing tension on the dollar-funding market is causing storms in markets to raise funds denominated in other currencies," Shirakawa told reporters, explaining why Japan was taking its place on the frontline.