TOKYO — Japan’s Financial Services Agency ordered brokerage SMBC Nikko Securities to suspend its block trading operations for three months from today as part of penalties in a market manipulation case.

That follows the arrest of its vice president, Toshihiro Sato, and several other employees on suspicion they put in massive buy orders to prop up stock prices of certain shares.

The company had already suspended its block trades due to the scandal. In a written statement it apologized and said it was taking the penalties “very seriously.” SMBC Nikko Securities and its parent company, Sumitomo Mitsui Financial Group, the country’s second-biggest financial group, also outlined plans for improving their governance.

The Securities and Exchange Surveillance Commission, the government body overseeing stock transactions, filed formal accusations against SMBC Nikko and its workers earlier this year of violating the Financial Instrument and Exchange Act.

The case involves big purchases of shares just before the market closed to push their prices higher with the intent of using those prices for clients’ block sales overnight.

The investigation into the transactions has taken a big bite out of the company’s revenue for fees and underwriting in this financial year.

Late in September, SMBC Nikko announced that regulators had recommended administrative penalties for making illegal share purchases aimed at manipulating prices; inadequate trade screening systems and management of block trade and “inappropriate” management of dealings between the brokerage and SMBC’s banking business. The company also recently set up a business risk control division.

On conviction, violations of the Financial Instrument and Exchange Act carry a maximum penalty of 10 years in prison, a 10 million yen ($82,000) fine, or both. A company faces a fine of up to 700 million ($5.8 million).