To bolster its defense, Danske, already under investigation in a number of countries, nominated former Dutch finance minister and ex-ABN Amro CEO Gerrit Zalm to its board.
Danske is being investigated in Denmark, Estonia, France and Britain over 200 billion euros ($226 billion) in payments found to have flowed through its Estonian branch from Russia, former Soviet states and elsewhere.
The SEC is now also carrying out inquiries, adding to an ongoing criminal investigation by the U.S. Department of Justice (DoJ) in relation to the case of possible money laundering at Danskeâ€™s Estonia branch.
The value of Denmarkâ€™s largest bank has almost halved since last March, with investors concerned by the threat of hefty fines. The news about a new investigation by the SEC pushed its shares down a further 3.7 percent by 1215 GMT.
Shares in Swedbank have also tumbled over the past two sessions after Swedish television linked the bank to the Baltic money laundering accusations.
Danske will also propose Christian Sagild, former head of Danish insurance firm Topdanmark, to the board at its March 18 annual shareholder meeting.
Nominating Zalm and Sagild to the board is the first concrete step by Karsten Dybvad, who took over as chairman in December.
Dybvad, former head of the main Danish business lobby group and a former government official, been tasked with appointing a new permanent chief executive after Thomas Borgen resigned in September last year.
â€śWe have no information about when the investigations conducted by DoJ and SEC are expected to be completed, nor do we know what the outcome of these will be,â€ť said interim CEO Jesper Nielsen.
The new investigation came only two days after Estoniaâ€™s financial regulator took the unexpected step of demanding that Danske close its branch there and repay customersâ€™ deposits within eight months, overturning the lenderâ€™s plan to scale back but keep business in the country.
($1 = 0.8830 euros)