The yen threatened to test ?160 to the dollar on Thursday as investors balanced the fundamentals, which suggest weakening, and the ever-present possibility that Japan and the United States will spend billions more propping up the currency.

¡°The yen¡¯s further weakening could prompt another coordinated intervention, so market caution will grow, which will likely put a floor under the yen,¡± said Tsuyoshi Ueno, executive research fellow at NLI Research Institute.

The coordinated intervention, which was undertaken in late July and confirmed by both governments, helped take the yen from about ?162.80 to the dollar to around ?155. It has since drifted back toward ?160 to the dollar.