The European Central Bank says it is going to buy the bonds of the debt-ridden countries in the euro currency union in hopes of easing their borrowing costs.

The bank set no limit Thursday on the volume of the bonds it plans to buy, Europe's latest effort to resolve the three-year debt crisis. The bank also kept its benchmark lending rate unchanged at three-quarters of one percent as the 17-nation eurozone economy continues to contract.

European and U.S. stock markets moved sharply higher after the central bank announced its bond-buying program.

Bank chief Mario Draghi said the bond purchases are aimed at ending sharp swings in interest rates for financially troubled countries, such as Spain and Italy, as they sell their bonds on world financial markets. The central bank hopes that its purchases of notes will not only stabilize the rates, but reduce them.

Draghi attributed the volatility of the European government bond market to “unfounded fears on the part of investors of the reversibility of the euro.” But he said the bank will do whatever it can to make sure the use of the euro does not end.

“We will do whatever it takes within our mandate, within our mandate to have a single monetary policy in the euro area and to maintain price stability in the euro area and to preserve the euro, and we say that the euro is irreversible.”

Although the central bank said there is no limit on the amount of national bonds it may purchase, the governments selling them must agree to repay those notes within three years.

Greece, Ireland and Portugal already have been forced to secure international bailouts, and similar assistance has been extended to Spain's beleaguered banks. Analysts have voiced fears that the Madrid and Rome governments could be next, since their borrowing costs until recently have approached the levels that forced the other countries to seek rescue packages.