Bloomberg reported that officials were divided in last month's meeting on whether to boost interest rates in June.
The holdings in exchange-traded products backed by the precious metal fell to a three-month low of 1616.1 tonnes, with traders are studying the economic data for more signals of a rate rise.
Copper prices may be on an upward trajectory this year, with Macquarie seeing the metal's three-month futures-for-delivery approaching $US6500 a tonne.
However, it also warns of a 6% fall of total output by copper miners this year if problems facing the industry continue. Natural disasters and labour disputes have reduced output by 280,000t.
Speculation of a Chinese stimulus package, coupled with lower supply, has lifted the copper price after it had dropped to a five-year low in January.