Sompo Japan Insurance Inc. said Monday it distributed misleading advertising in the early 1990s, causing some buyers of its savings-type policies to believe they would get higher returns than were available.

The announcement, based on internal findings, said Sompo Japan's ads left out the fact that the return to be received when policies were due would depend on prevailing interest rates.

The findings were the result of an internal investigation the insurer conducted after the discovery of a similar problem at Aioi Insurance Co.

Sompo Japan stopped short of making clear how many policyholders were affected by its misleading advertising.

"We have just begun our probe, so we have yet to get all the facts about the entire affair," said Sompo Japan's public relations officer.

This could mean similarly questionable methods may have been used to promote other insurance policies, industry observers said.

Last Friday, Aioi said it will pay additional sums upon customer request in order to offer returns tied to interest rates that prevailed at the time of policy purchases, which were much higher than today's rates, as suggested in its ads.

Such costs, which will cover some 20,000 policies, might run up to 20 billion yen.