The Federal Reserve looks set to continue buying bonds to stimulate economic growth over coming months despite rising concern about the risks of the policy inside the central bank.

Minutes from the Fed's December meeting showed a growing reticence about further increases in the central bank's $2.9 trillion balance sheet, which it expanded sharply in response to the financial crisis and recession of 2007-2009.

"Several (officials) thought that it would probably be appropriate to slow or to stop purchases well before the end of 2013, citing concerns about financial stability or the size of the balance sheet," the minutes said.

Still, the Fed appeared likely to continue buying assets for the foreseeable future, having announced in December it was extending monthly purchases of $40 billion in mortgage securities and also buying $45 billion in Treasuries each month.

A few of the voting members on the central bank's policy-setting Federal Open Market Committee thought asset buying would be warranted until about the end of 2013. A few others highlighted the need for further large-scale stimulus but did not specify an amount or time frame.

Fed officials generally agreed that the labor market outlook was not likely to improve without further nudging from the monetary authorities.

The U.S. economy expanded a respectable 3.1 percent in the third quarter on an annualized basis, but growth is believed to have slowed sharply to barely above 1 percent in the last three months of the year.

Data on Thursday showed a solid gain of 215,000 new private sector jobs for December, while analysts polled by Reuters last week were looking for a rise of 150,000 new jobs in the Labor Department's official survey, due out on Friday.

(Reporting by Pedro da Costa; Editing by Andrea Ricci)