Several policymakers at the US Federal Reserve expressed concern about the risks coming from its efforts to boost the US economy by keeping borrowing costs low for the foreseeable future.

Minutes of the institution's 29-30 January policy meeting showed that some officials worried about monthly purchases of $85 billion a month in Treasury and mortgage bonds.

They expressed concern that the continued purchases could eventually escalate inflation, unsettle financial markets or cause the Fed to absorb losses once it begins selling its investment holdings.

In the end, the Fed voted last month to keep its bond program open-ended and at the same size.

The Fed said in a statement that the bond purchases would continue until the job market improved substantially.