Warren Buffett says the wealthy are 'undertaxed' compared to the rest of the US population

Warren Buffett spoke with on Monday with CNBC's Becky Quick on " Squawk Box." Buffett's comments come after Berkshire Hathaway released its fourth-quarter earnings and after Buffett put out his annual letter to shareholders. In the letter, Buffett said he hoped to make an "elephant-size" purchase, but added that current prices are "sky-high.