The Federal Reserve bought $12 billion net of agency mortgage-backed securities in the latest week, the New York Fed said on its Web site on Thursday.

The amount is down from the previous week's net purchases of $14 billion.

The purchases brought the U.S. central bank's purchase of mortgage bonds guaranteed by Fannie Mae, Freddie Mac and Ginnie Mae to roughly $1.149 trillion since January 2009.

The Fed said it bought $16.359 billion gross of agency MBS from Jan. 14 through Jan. 20.

At the same time, it sold $4.359 billion of mortgage securities.

The Fed aims to buy $1.25 trillion of agency MBS in a bid to bring down mortgage rates and to stimulate the battered housing sector and the overall economy.