Billionaire U.S. investor Warren Buffett has nudged up his stake in world No.3 retailer Tesco , a person familiar with the matter said, in what could be seen as a vote of confidence in new chief executive Phil Clarke.

Buffett's Berkshire Hathway last month bought around 34 million Tesco shares for about 120 million pounds ($185 million), lifting its stake in the British supermarket group to 3.64 percent from 3.21 percent, the person said.

Tesco declined to comment. Berkshire Hathaway could not immediately be reached for comment.

Earlier this year, Buffett caused a stir by saying he thought Tesco should "look hard" at its loss-making Fresh & Easy chain in the United States.

Clarke, who succeeded long-serving predecessor Terry Leahy in March, has laid out a plan for the chain to significantly reduce its losses this financial year and break even towards the end of fiscal 2012-3, and made changes such as introducing fresh bakery products and coffee and testing a loyalty card.