Copper is often used as a gauge of global economic health and a policy tightening might slow a recovery in the world's biggest economy and boost the dollar
Three-month copper on the London Metal Exchange (LME) had climbed 1pc to $9,534.50 a tonne by 1615 GMT, on track to finish the week in positive territory.
The metal was still up around 7pc for the April-June quarter, however - the fifth consecutive quarter of rising prices - after reaching an all-time peak of $10,747.50 on May 10.