Fears that Greece will need to leave the single currency union pushed the dollar to a four-month high against the euro Thursday.
The dollar index, which measures the dollar against a basket of six currencies, jumped to its highest level since Sept. 2010.
The U.S. currency has been rising against the euro ever since Greece held elections in early May. Greek voters gave support to anti-austerity parties, but politicians failed to create a new government. As a result, Greece will be holding another round of elections June 17.
Traders are worried that if those anti-austerity parties win in June the country may drop out of the euro zone, which could hurt the euro's credibility and roil financial markets.
The euro fell to $1.2714 in late trading Thursday from $1.2725 late Wednesday. The euro fell as low as $1.2665 earlier, its lowest point since Jan. 16. The euro has fallen about 3 percent against the dollar since the Greek elections May 6.
In other trading Thursday, the British pound fell to $1.5816 from $1.5917. The dollar rose to 0.9447 Swiss franc and to 0.9437 Swiss franc and to 1.0174 Canadian dollar from 1.0112 Canadian dollar.
The dollar fell to 79.28 Japanese yen from 80.29 yen.