Buffett mum on two big stock investments

By Jonathan Stempel

NEW YORK (Reuters) - Warren Buffett said he has bought large stakes in two companies' stocks, but would not identify the firms as he continues to accumulate their shares.

"We don't itemize the two securities referred to, which have a market value of $1.9 billion, because we continue to buy them," the billionaire U.S. investor wrote in his annual shareholder letter on Thursday.

"I could, of course, tell you their names," added Buffett. "But then I would have to kill you."

Regulators sometimes allow Berkshire Hathaway Inc. (BRKa.N) (BRKb.N), the holding company that Buffett controls, to delay disclosing some equity purchases so that investors cannot copy Buffett before he has finished amassing meaningful stakes.

In his shareholder letter, the world's second-richest person revealed that Berkshire had taken a 4 percent stake in Posco (005490.KS), sending the South Korean steelmaker's shares up more than 3 percent in Friday trading.

And in February, Berkshire revealed that it had bought some 1.3 percent of U.S. Bancorp (USB.N), the sixth-largest U.S. bank -- but had started to buy shares in the first quarter of 2006.

In his letter, Buffett said Berkshire has $61.53 billion of common stock investments. He listed 17 companies in which Omaha, Nebraska-based Berkshire has investments topping $700 million, led by a $9.65 billion stake in Coca-Cola Co. (KO.N).

Buffett said there are two other companies in this category. He wouldn't say which.

Buffett's 22-page shareholder letter is filled with discussions of Berkshire's operations, economic and governance issues, and many lighthearted anecdotes and asides.