Denmark's public prosecutor for serious economic and international crime is investigating Danske Bank over price manipulation of a particularly serious nature, the bank said on Friday.
This has also been confirmed by the public prosecutor.
The bank said four employees from the banking operation and its mortgage lending unit Realkredit Danmark violated internal rules and may potentially have manipulated prices.
It said that it had found no evidence that other staff members were involved in the transactions. The four employees and their two superiors have been suspended, it said.
"We consider the matter to be very serious and are cooperating fully with the authorities," Chief Executive Thomas Borgen said in the announcement.