The ECB took financial markets by surprise by cutting its central "refi" or refinancing rate by a quarter of a percentage point to a new record low of 0.25 per cent.
Speculation of a pending rate cut had briefly surged when new data showed eurozone inflation slowing unexpectedly to a four-year low of 0.7 per cent last month, raising the spectre of deflation.
Nevertheless, most ECB watchers had thought the bank would keep its gunpowder dry at its monthly policy meeting at least until next time, when it would have compiled new inflation and growth forecasts.
The euro fell sharply against the dollar on the news.
