* Dollar/yen stays on defensive, hits fresh 18-month low
* Aussie holds firm ahead of RBA decision later on Tuesday
* Dollar index touches lowest since January 2015
By Masayuki Kitano
SINGAPORE, May 3 (Reuters) - The dollar set a fresh 18-month low versus the yen on Tuesday, as the yen pushed higher in a holiday-thinned market, while the Australian dollar held firm ahead of an interest rate decision from Australia's central bank.
The dollar fell 0.3 percent to 106.09 yen JPY= , and fell to as low as 106.05 yen at one point, its lowest level since October 2014.
A Singapore-based trader said there appeared to some speculative yen buying in thin conditions with Japanese markets closed from Tuesday to Thursday for public holidays.
The yen added to its recent gains, having jumped about 5 percent against the dollar last week as the Bank of Japan held off from expanding its monetary stimulus - the yen's biggest weekly gain since 2008.
The Japanese currency has risen further this week after the U.S. Treasury on Friday put Japan on a new currency monitoring list with four other countries that have large trade surpluses with the United States.
The report by the U.S. Treasury was seen as making it harder for Japan to intervene in the currency market to stem the yen's gains. greenback inched lower against a basket of six major currencies and slipped to a low of 92.472 .DXY at one point, its lowest level since January 2015.
The euro touched its strongest level since last August at $1.1540 EUR= . The euro last traded at $1.1536, steady on the day.
The greenback has fallen since mid-March when Federal Reserve Chair Janet Yellen signalled the Fed would proceed cautiously with further rate increases given global risk and domestic inflation stuck below the central bank's 2 percent goal.
The Australian dollar edged up 0.1 percent to $0.7677 AUD=D4 , with all eyes on the interest rate decision from the Reserve Bank of Australia later on Tuesday.
While a majority of economists polled by Reuters expect no rate move, a growing number are forecasting a cut following some soft inflation numbers. AU/INT