The Fed released minutes of its December 16-17 meeting on Wednesday. Investors had expected to get insight into when the Fed will start to hike its interest rate. Minutes showed that the Fed is unlikely to hike its interest rate before April.

Analysts expect the first interest rate hike by the Fed in the mid-2015.

The Fed policymakers said that the Fed could start to hike its interest rate before inflation will pick up. But they added that "they would want to be reasonably confident that inflation will move" back toward the Fed's 2% inflation target.

The Fed's preferred gauge, the personal consumption expenditures price index (PCE), increased at annual rate of 1.2% in November. The PCE price index excluding food and energy costs rose 1.4%.

Many Fed officials think a global economic slowdown is "an important source of downside risks to domestic real activity and employment".

The net effect of falling oil prices was "anticipated to be positive", the officials said. They believe that falling oil prices won't impact their decision on interest rate hike.

Most Fed officials agreed that "it will be appropriate to raise the target federal funds rate fairly gradually".