The Seibu group's secretive reputation was further underscored Monday, as Seibu Railway Co. declined to give details about a managing director's resignation last week over his involvement in questionable sales of its shares.

Seibu Railway's parent, Kokudo Corp., has been embroiled in an insider trading scandal in which the company allegedly sold Seibu Railway shares without disclosing potentially damaging information.

Seibu Railway held a news conference Monday after strong requests from the media, which demanded details of the resignation Friday of Toshiyuki Shirayanagi.

The firm on Friday issued only a brief press release, saying Shirayanagi tendered his resignation to take responsibility for his involvement in Kokudo's attempts to sell some of its Seibu Railway shares.

Another Seibu Railway managing director, Noriaki Mayuzumi, told the news conference that Shirayanagi introduced 11 companies to Kokudo and nine of them agreed to buy Seibu Railway shares.

But Mayuzumi declined to give further details, including the names of the nine buyers and the dates the transactions, saying the matter was under investigation by authorities.

Kokudo, a privately held company, is effectively a controlling entity of the Seibu group, which operates railways, hotels, and sports and leisure businesses, as well as the Seibu Lions pro baseball team, which on Monday won this year's Japan Series.

The firm's problems came to light earlier this month, when it announced it had owned more shares in Seibu Railway than it had been reporting to authorities for years.

The true size of the Kokudo's stake meant that Seibu Railway shares could have been delisted from the TSE, which bars heavy concentration of ownership to ensure liquidity.