The Japanese yen rallied to a fresh eighteen-month high on Tuesday with the US dollar trading last at 106.21 yen, down 0.2 percent so far. The greenback fell to as low as 106.05 yen at one point, its lowest level since October 2014. Investors are showing concern that global central banks are unable to boost growth through aggressive policy easing.

According to Cliff Tan, East Asia head of global markets research at Bank of Tokyo-Mitsubishi UFJ Ltd, "Markets are telling us that the European Central Bank and the Bank of Japan are failing in their mission to expand monetary stimulus and that these policies are not doing what they are expected to do.”

Yen Up 5%

The yen added to its recent gains, having jumped about 5 percent against the dollar last week-- the yen's biggest weekly gain since 2008--as the Bank of Japan held off from expanding its monetary stimulus after the U.S. Treasury put Japan on a new currency monitoring list on Friday along with four other countries that have large trade surpluses with the United States.

Japan is currently celebrated its Golden Week series of holidays. Markets were closed on Friday and will be closed on Tuesday to Thursday this week.

The dollar index, which measures the dollar's performance against a trade-weighted basket of its peers, is trading at its lowest since January 2015 and has fallen about 6.2 percent so far this year. The currency has been under pressure while the U.S. Federal Reserve takes its time deciding to raise interest rates.