The Financial Services Agency on Friday ordered Nomura Securities Co. to improve its internal controls to prevent further insider trading, but fell short of instructing Japan's largest brokerage to suspend operations.

The agency's leniency was apparently due to the resignation of senior officials at its parent company, Nomura Holdings Inc., to take responsibility for the scandal, which the government said shook investors' trust in the nation's financial markets.

The administrative order focused on Nomura Securities' flawed internal controls, including insufficient compliance procedures and its failure to establish a firewall between its investment banking and brokerage divisions.