The Federal Reserve bought $25.45 billion net of agency mortgage-backed securities in the latest week, the New York Fed said on its website on Thursday.

That was up from the previous week's net purchases of $18.8 billion.

The purchases brought the U.S. central bank's purchase of mortgage bonds guaranteed by Fannie Mae, Freddie Mac and the Federal Home Loan Bank system to roughly $861.9 billion since January.

The Fed said it bought $31.22 billion gross of agency MBS from September 10 through September 16. At the same time, it sold $5.77 billion in mortgage securities.

The Fed aims to buy up to $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.