Japanese firms have been so busy paying top dollar in overseas acquisitions that sellers looking to offload assets in Asia now expect them to pay over the odds, according to the head of the country's biggest insurer, Tokio Marine Holdings Inc (8766.T).

Drive by a need to diversify exposure to natural disasters geographically, Tokio Marine president Tsuyoshi Nagano said his firm is still scouring markets around the world, including Latin America, for acquisition prospects. With insurers among the most acquisitive Japanese companies, Tokio Marine alone has spent more than $8 billion on international deals since 2008.

Still, rising prices have made the company more cautious in the Asia-Pacific region, he said, leaving few attractive deal prospects and price tags not matched by asset valuations. "In Asia, it has been widely established that Japanese companies are ready to pay high prices and sellers expect that when dealing with us," in an interview with Reuters.

Nagano declined to comment on whether Tokio Marine, Japan's biggest insurer by market capitalization, will make an offer for a stake now for sale in the life insurance unit of Bank Rakyat Indonesia (BBRI.JK). The Indonesia stake would give its buyer access to one of the world's most under-insured markets.

The Japanese firm's previous acquisitions include U.S. insurer Philadelphia Consolidated for $4.7 billion and Lloyd's of London insurer Kiln for $671 million in 2008, and U.S. business Delphi for about $2.7 billion in 2012.

But Nagano said Tokio Marine also needs to find other ways to expand its overseas businesses, including bancassurance deals to sell its insurance products at local banks' branches.

He said efforts to diversify risk exposure extend to its investment portfolio and the company will continue to reduce holdings of client companies' stocks, which were bought to cement business ties.

Japanese companies are under growing pressure to justify or reduce such holdings, as the practice has long been criticized for making companies vulnerable to stock market swings. The company 2.8 trillion yen ($22.45 billion) worth of these holdings, about 13 percent of total assets, and Nagano said the company aims to reduce that level to below 10 percent.

"Stocks are also very volatile. In our overall risk portfolio, their risks are greater than others, but returns are lower," he said.