Orajit Singkhalavanich, director-general of the Business Development Department, said that documents turned in earlier and previous explanations by the bank's representative had been insufficient to quell the department's concerns over the use of proxies in the transaction. The bank has until April 21 to fork over the paperwork.

"There are still doubts and unanswered questions about whether the sale of Shin shares had been done through nominees," said Orajit.

She added that the department, therefore, asked for the additional financial documents that were executed after the change in the shareholding structures of Cedar Holdings and Kularb Kaew, which are indirect shareholders of Shin Corp. Orajit added that after receiving these documents, the department would know who to invite to give further information.

Kularb Kaew is alleged to be a nominee of Temasek Holdings. Though Thais own 51 per cent of the company they have less than 10 per cent of the voting rights.

Kularb Kaew counts among its Thai shareholders Pong Sarasin, who is Shin's chairman. But according to the company's books, Thai shareholders are entitled to only 3 per cent of profits and only 5.1 per cent of the voting rights. If it were proven to be a nominee, the company would be in violation of the foreign business law which treats a foreign-owned company differently from a Thai-owned firm.

Under foreign-business laws, foreign entities must obtain business licences from the Commerce Ministry before making any investment in the Kingdom and must produce an investment plan to show how much they plan to invest in the next three years. After petitioning for a licence, they must bring in at least a quarter of the promised investment.

Kularb Kaew's shareholding structure was changed March 10. Its paid-up capital is Bt4 billion, divided into 400 million common shares. As a result of the change, Pong Sarasin has only 5.09 million preferred shares and Suphadej Poonpipat 3.28 million.

Since then, the company has added a new shareholder, Datuk Surin Upatkul, holding one preferred share and 272 million common shares. The remaining shares are held by Cypress Holdings, consisting of 8.05 million preferred shares and 111.56 million common shares.