The Swiss central bank imposed a ceiling on the franc's exchange rate for the first time in more than three decades and pledged to defend the target with the "utmost determination."

The Swiss National Bank is "aiming for a substantial and sustained weakening of the franc," the Zurich-based bank said in an e-mailed statement today. "With immediate effect, it will no longer tolerate a euro-franc exchange rate below the minimum rate of 1.20 francs" and "is prepared to buy foreign currency in unlimited quantities."

The franc has surged to records against the euro and the dollar, hurting exports and eroding economic growth. While the SNB last month boosted liquidity to the money market and lowered borrowing costs to zero, investor concern that governments may struggle to contain Europe's worsening debt crisis has continued to push the currency higher.