Warren Buffett’s Berkshire Hathaway Inc. bought roughly US$813 million worth of Bank of America Corp. stock, piling more funds into the lender amid its 31 per cent slump this year.

Berkshire purchased roughly 33.9 million of the company’s shares this week, boosting its stake by more than 3 per cent to about 981.7 million shares, according to a regulatory filing Wednesday. Buffett’s conglomerate added the shares at an average price of US$23.99.

Berkshire is ramping up its bet on Bank of America after receiving the green light from the Federal Reserve when its holdings surpassed a 10 per cent ownership level, a key threshold requiring regulatory review. Buffett asked policy makers last year for permission to boost the stake, and the Federal Reserve Bank of Richmond issued a no-objection letter on April 20, according to a spokesperson.

Berkshire’s Bank of America stake, which started from preferred stock and warrants, has transformed into one of the Omaha, Nebraska-based conglomerate’s largest holdings. At the end of March, it was Berkshire’s second-largest by market value, behind Apple Inc.

Berkshire, which invests in multiple banks, reduced some of those holdings in the first quarter, including wagers on Goldman Sachs Group Inc. and JPMorgan Chase & Co. The firm will report second-quarter changes to those stakes within the next month.