With the Bank of Japan holding off further stimulus and concerns over the “Brexit” vote fueling safe-haven bets, the Japanese yen and currency-related exchange traded funds surged Thursday.

On Thursday, the CurrencyShares Japanese Yen Trust (NYSEArca: FXY) jumped 1.6% while the ProShares Ultra Yen (NYSEArca: YCL), which tries to reflect the daily 2x or 200% return of the the U.S. dollar price of the yen, increased 1.7%. Year-to-date, FXY rose 13.2% and YCL gained 27.8%.

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The yen currency appreciated to ¥104.22 per U.S. dollar on Thursday, its highest level in almost two-years.

The yen currency strengthened after the Bank of Japan said it would wait on taking further action until the results of the British referendum or so-called Brexit vote next week, the Wall Street Journal reports.

People close to the BOJ hinted that even if the central bank acted this week, the market impact may be limited if a Brexit vote sent shocks around global markets.

The JPY, which has traditionally acted as a global safe-haven play in times of duress, could continue to appreciate if the Brexit vote passes and drags on financial markets.

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