Four of Japan's six major nonlife insurance companies saw their group net profits plunge in business 2007 as the U.S. subprime loan crisis and the subsequent fall in global stock prices pushed down profits from their investments, the firms said Wednesday.

Aioi Insurance Co., which suffered the most from the housing loan upheaval, booked ¥83.6 billion in subprime-related losses in the business year ended in March. As a result, Aioi posted a net loss of ¥3.17 billion, down from a net profit of ¥16.2 billion the year before.

"One of the reasons we booked a group net loss was because of the great amount of losses we suffered from the subprime loans," Aioi Managing Director Takayoshi Uemura said. "We are strengthening divisions to monitor investment polices."