The Financial Supervisory Agency on Thursday conducted a surprise inspection of Japan's largest life insurer, Nippon Life Insurance Co., the latest in a series of inspections of life insurers, sources close to Nippon Life said.

The FSA, Japan's financial watchdog, is expected to look into the quality of assets held by Nippon Life and whether the firm has tried to convince customers to change policies from one type to another midway through a contract without providing details about new policies.

The agency did not elaborate on the purpose of the examinations, the sources said.

Thursday's inspection follows similar examinations of Fukoku Mutual Life Insurance Co. and Orix Life Insurance Corp. in January.

The FSA plans to complete inspections of all life insurers in Japan by the end of June.