The dollar rose sharply against the yen and other currencies on day as North Korea announced it had conducted its first ever nuclear test.
The dollar jumped to 119.96 yen in late morning Asian trade as Pyongyang's official Korean Central News Agency announced the test.
Late Friday in New York, the dollar was trading at 118.98, a seven-month high against the yen.
The euro weakened to $ 1.2596 from $ 1.2598 in late New York trades when the dollar rose to its best level since July against the single European currency.
Tokyo's markets were closed for a public holiday.
"No one is sure exactly what is going on," said Thomas Lam, treasury economist with United Oveseas Bank Group.
He warned that if developments intensified on the Korean peninsula, the dollar-yen would probably be most at risk.
The South Korean won was down sharply against the dollar, falling to 959 levels from around 949 on Friday as the Seoul bourse lost 2.75 percent.