Mario Draghi, president of the European Central Bank, has unveiled details of a new bond-buying plan aimed at easing the eurozone's debt crisis.
He said the scheme would provide a "fully effective backstop" and that the euro was "irreversible".
The ECB aims to cut the borrowing costs of debt-burdened eurozone members by buying their bonds.
The Spanish government's implied borrowing costs fell sharply after the announcement.
Mr Draghi said the ECB would engage in outright monetary transactions, or OMTs, to address "severe distortions" in government bond markets based on "unfounded fears".
He insisted that the ECB was "strictly within our mandate" of maintaining financial stability, but reiterated the need for governments to continue with their deficit reduction plans and labour market reforms.
