The U.S. Federal Reserve's balance sheet grew to a record size in the latest week, spurred by its $600 billion bond-buying program aimed to support economic growth, Fed data released on Thursday showed.

The Federal Reserve headquarters in Washington, DC.

The balance sheet — a broad gauge of Fed lending to the financial system — expanded to $2.452 trillion in the week ended Feb. 2 from $2.426 trillion the prior week.

It narrowly surpassed the prior record of $2.451 trillion set three weeks ago as it has been buying Treasurys with the goal of stimulating investments and holding down borrowing costs. This second round of Fed bond purchases, or 'quantitative easing,' dubbed QE2, began last November.

The central bank's holding of U.S. government securities jumped to $1.138 trillion on Wednesday from last week's $1.114 trillion total.

Meanwhile, the Fed's ownership of mortgage-backed bonds guaranteed byFannie Mae, Freddie Mac and the Government National Mortgage Association (Ginnie Mae) held steady at $965.08 billion in the latest week.

The Fed's holdings of debt issued by Fannie Mae, Freddie Mac and the Federal Home Loan Bank system totaled $144.62 billion, unchanged from a week earlier.

Meanwhile, the Fed's overnight direct loans to credit-worthy banks via its discount window averaged $51 million a day in the week ended Wednesday, faster than the $39 million daily pace reported last week.