Shares of Japanese trading houses rose on Tuesday after Warren Buffett, chairman and CEO of Berkshire Hathaway, raised his stakes in the firms and said he may increase his holdings even further.

In an interview with Nikkei, Buffett said he is considering additional investment in five major Japanese trading houses, adding that he was “very proud” of his existing investments in them.

Shares of Mitsubishi Corp. rose 2.08% in Japan’s afternoon trade, Mitsui & Co. gained 2.66%, Itochu Corp climbed 2.98% and Marubeni Corp. advanced 4.55%. Sumitomo Corp. also rose 3.19%.

Berkshire Hathaway has raised its stakes in all five trading houses to 7.4%, according to CNBC’s Becky Quick. That’s up from positions of 6.6% in Mitsubishi Corp., 6.6% in Mitsui & Co., 6.2% in Itochu Corp., 6.8%  in Marubeni Corp. and 6.6% in Sumitomo Corp, according to November filings.

Buffett told Nikkei that he is planning to meet with the companies later in the week “to really just have a discussion around their businesses and emphasize our support,” according to the report.

Japan’s five largest trading companies — known as sogo shosha — are conglomerates that import everything from energy and metals to food and textiles into resource-scarce Japan. They also provide services to manufacturers. The trading houses have helped grow the Japanese economy and contributed to the globalization of its business.

Late last year, Berkshire Hathaway increased its positions in the five leading trading houses in Japan by at least 1 percentage point to more than 6% each — after its initial purchase in August, when Buffett acquired stakes worth more than $6 billion in total on his 90th birthday.

Nikkei separately reported that Buffett’s Berkshire Hathaway is preparing another issuance of yen-denominated bonds, which was seen as a signal the conglomerate would increase its investments in Japan.

Buffett will be live from Japan on CNBC’s U.S. “Squawk Box” on Wednesday to discuss his investments in the country.

— CNBC’s Becky Quick contributed to this report