The Federal Reserve's balance sheet expanded to a record size in the latest week, as the central bank bought more bonds in an effort to support the economy, Fed data released on Thursday showed.

The purchase was part of its $600 billion program, dubbed QE2, aimed at stimulating investment and economic activity.

The balance sheet -- a broad gauge of Fed lending to the financial system -- swelled to $2.841 trillion in the week ended June 22 from $2.811 trillion the prior week.

(Reporting by Emily Flitter; Editing by James Dalgleish)