The euro jumped to its strongest level against the dollar in more than two years on Friday as banks adjusted positions for the year end, while the yen hit five-year lows for a second straight session.
The dollar was broadly weaker against European currencies, including the euro, sterling and Swiss franc. Thin liquidity likely helped exaggerate market moves.
The European Central Bank will take a snapshot of the capital positions of the region's banks at the end of 2013 for an asset-quality review (AQR) next year to work out which of them will need fresh funds.
This has created some demand for euros to help shore up their balance sheets, traders said.
(Read more: Could dollar-yen hit 125 next year?)