The Norwegian government is the bank's top owner with a stake of 34 percent.
Norway's biggest bank DNB must provide a written explanation of its policy of helping clients set up offshore companies in the Seychelles, the Norwegian industry minister said in a statement on Monday.
"DNB says this should not have happened and that the bank should not have participated. That I agree to," Trade and Industry Minister Monica Maeland said.
The Norwegian government is the bank's top owner with a stake of 34 percent. DNB's Seychelles activities were first reported by daily Aftenposten, quoting leaked documents from Panama-based law firm Mossack Fonseca.
The leak involves more than 11.5 million documents from the files of the law firm, revealing details of hundreds of thousands of clients in multiple jurisdictions.
DNB said in a separate statement it regretted assisting about 40 customers in setting up the firms between 2006 and 2010, and that the practice had ended.
"It's the customers' responsibility to report their own funds to tax authorities. Still, we believe we should not have contributed to establishing these companies," Chief Executive Rune Bjerke said, referring to the Seychelles firms.
"The structures could be abused for tax evasion," the CEO added.
Bjerke said an internal investigation would be conducted and he would later give a briefing to the bank's board.