Trading house Mitsubishi Corp. said Wednesday it will shut down a Singapore unit that trades crude oil and petroleum products after alleging earlier that a trader racked up $320 million of losses in unauthorized trading.

Mitsubishi said the unit, Petro-Diamond Singapore, "has confirmed after closing the positions concerned, it will realize a loss of approximately ¥34.2 billion ($314 million) before taxes, which could put the subsidiaries final debt as high as ¥30.8 billion."

Mitsubishi Corp., Japan's biggest trading house by sales, said in September the trader at Petro-Diamond had lost $320 million through unauthorized transactions in crude oil derivatives and that the matter had been reported to the police.

The trader later denied wrongdoing in a statement issued through a lawyer.