The dollar fell to a 15-month low against the yen on Monday as a renewed slide in oil prices and doubts about the effectiveness of the Bank of Japan's negative interest-rate policy drove investors back into the safe-haven currency.
After gaining overnight, crude oil futures again fell, weighing on investor confidence and sapping risk appetite.
The surprise announcement on Jan. 29 that the BoJ was cutting its interest rate to minus 0.1 percent on certain deposits sent the dollar up as much as 2 percent. But markets have since reconsidered, with investors now buying the yen and selling the dollar.
Imposing negative rates was expected to weaken the yen as investors would essentially have to pay to hold money with Japan's central bank. But the small scale of the policy, only affecting certain deposits, and continued fears of a global economic slowdown have overpowered the bank's action.