The euro rose 2 percent against the dollar on Thursday in its biggest one-day percentage gain since May 19 at current prices.
The euro was supported after European banks borrowed less money than expected from a European Central Bank's tender, cooling concerns over euro zone banks' funding issues.
Madrid's ability to sell five-year bonds following Moody's Investors Service decision on Wednesday to put Spain's sovereign rating on review for possible downgrade added to euro optimism.
The euro was last at US$1.2479 after climbing as high as $1.2484. (Reporting by Nick Olivari)