TOKYO, Jan 12 (Reuters) - Japan's financial regulator on Friday ordered SBI Securities to halt part of its business related to initial public offerings (IPOs) for a week through Jan. 18 as a penalty for having manipulated clients' post-IPO share prices.

The Financial Service Agency also ordered the online brokerage unit of financial conglomerate SBI Holdings to improve the group's compliance.

The Securities and Exchange Surveillance Committee (SESC) has found that SBI aimed to boost opening prices of three stocks for which it served as lead underwriter by asking investor clients to buy shares in them at the offering price, knowing the orders would not reflect market conditions.

SBI said in a statement that the company would take the administrative order seriously and work to beef up its internal compliance to present recurrences and regain public trust. (Reporting by Makiko Yamazaki; Editing by Muralikumar Anantharaman)