The Federal Reserve is expected to keep interest rates unchanged tonight and may struggle to convince skeptical investors it can tighten monetary policy before the end of the year in the face of US and global economic headwinds.

The world's most powerful central bank hasn't hiked rates in about a decade and markets see virtually no chance it will do so at the end of this week's two-day policy meeting. The Fed is scheduled to announce its rate decision at 5am tomorrow morning, Sydney time.

A spate of dismal data on the US and global economies has fuelled a public row between Fed Chair Janet Yellen and fellow policymakers, igniting speculation the central bank will wait until 2016 to begin its "liftoff" from near-zero rates.

Forty-six economists polled by Reuters unanimously expect the Fed to keep its target rate for overnight lending between banks steady at 0 per cent to 0.25 per cent tonight, as it has since 2008 when it embarked on an effort to nurse the economy back from a severe recession.