The US Federal Reserve is expected to keep interest rates unchanged as it continues to monitor the impact of weakening global growth. It may also be trying to give markets a sign that it's determined to resume policy tightening this year.

The Fed has held its overnight lending rate for banks at a target range of between 0.25 and 0.50 percent, since it lifted the benchmark interest rate for the first time in a decade from near zero last December.

Since then the Fed has signaled more caution, as concerns a slowing China would bring challenges to global growth sparked stock price declines and tighter financial market conditions earlier in the year.