While the companies did not name the client, the revelation comes as global banks, including Credit Suisse, have warned of a fall-out from the downfall of hedge fund Archegos Capital.
"I don't expect that the loss at Nomura and Mitsubishi will cause bigger problems such as that it would greatly undermine their financial health or it will make it difficult to perform their duties," Aso told reporters after a cabinet meeting.
"We are looking into the matter now. The Financial Services Agency will share information with the Bank of Japan and overseas authorities from now on as well," he said on Friday.
"We must closely watch the situation."
Aso declined to comment further, saying the incident was a matter regarding individual private financial institutions.
While government officials have brushed aside the risk the matter could trigger a financial crisis, some remain wary.
"When incidents of this kind happened in the past, we treated them as 'individual cases' and neglected to fully take precaution," a government official said on condition of anonymity. "Some of them later morphed into financial crisis."
(Reporting by Tetsushi Kajimoto; Editing by Himani Sarkar)
(Only the headline and picture of this report may have been reworked by the Business Standard staff; the rest of the content is auto-generated from a syndicated feed.)
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