The Bank of Japan held off on expanding monetary stimulus, as Gov. Haruhiko Kuroda and his colleagues opted to take more time to assess the impact of negative interest rates.

The move comes as a surprise to the slight majority of economists surveyed by Bloomberg who had projected some action from the central bank in response to a strengthening in the yen that has cast a shadow over prospects for higher wages and investment. The currency rallied against the dollar immediately after the decision while stocks in Tokyo tumbled.

Policy makers are betting that their success in bringing down borrowing costs since unveiling the negative-rate strategy in January will generate an acceleration in lending. They left unchanged three key easing tools — the ¥80 trillion target for expanding the monetary base, mostly through government-bond purchases, the 0.1 percent negative rate on a portion of the cash banks park at the BOJ, and a program to buy riskier assets including stocks. Separately, they postponed their time frame for reaching a 2 percent inflation target, to sometime in fiscal 2017, for the fourth delay in about a year.