The Fed released its July monetary policy meeting minutes on Wednesday. There was no clear signal of when the Fed will start raising its interest rate, but there were doubts about the interest rate hike in September.

"Most judged that the conditions for policy firming had not yet been achieved, but they noted that conditions were approaching that point. Participants observed that the labour market had improved notably since early this year, but many saw scope for some further improvement," the minutes said.

Fed officials were concerned about the pace of inflation. According to the minutes, "almost all members indicating that they would need to see more evidence that economic growth was sufficiently strong and labour markets conditions had firmed enough for them to feel reasonably confident" that inflation would return to the Fed's 2% target over the medium term.

Several members were concerned over the situation in China.

"While the recent Chinese stock market decline seemed to have had limited implications to date for the growth outlook in China, several participants noted that a material slowdown in Chinese economic activity could pose risks to the U.S. economic outlook," the minutes said.

Fed officials said that low exports due to the strong U.S. dollar would continue to weigh on economic growth in the second half of 2015.

Some Fed officials "were concerned about the outlook for consumer spending, noting that spending had been disappointing in recent months even though real income had already been boosted by the lower gasoline prices and the improved labour market".