TOKYO (Reuters) -Warren Buffett's Berkshire Hathaway ( BRK/A ) raised its holdings in five Japanese trading houses, regulatory filings showed on Monday, in the U.S. conglomerate's latest investments in Japan's top commodity firms that began nearly five years ago.

Berkshire's stake in Mitsui & Co ( MITSF ) rose to 9.82% from 8.09%, while its holdings in Mitsubishi Corp ( MSBHF ), Sumitomo Corp ( SSUMF ), Itochu ( ITOCF ) and Marubeni ( MARUF ) also rose by some percentage points, according to documents filed to Japan's securities watchdog by its unit, National Indemnity Company.

The filings followed Buffett's annual letter to Berkshire shareholders last month, where he said the five trading houses agreed to "moderately relax" limits that capped Berkshire's ownership stakes below 10%.

"Over time, you will likely see Berkshire's ownership of all five increase somewhat," Buffett had written.

Known as "sogo shosha", the trading houses deal in a variety of materials, products and food - often serving as intermediaries - and provide logistical support. They are also involved in the shipping, energy and metals businesses.

(Reporting by Tokyo Newsroom; Editing by Muralikumar Anantharaman)