Norway's Prime Minister Erna Solberg says the United States has given assurances it had stopped spying on its allies in 2014, after officials in Oslo launched a protest against the surveillance.
Norway called in the US ambassador, she said, after a report that the US National Security Agency had used a partnership with Denmark's foreign intelligence unit to spy on senior officials including herself.
NATO members Norway and Denmark are close US allies.
Denmark hosts several key landing stations for subsea internet cables to and from Sweden, Norway, Germany, the Netherlands and the United Kingdom.
"I am glad that the Americans clearly expressed that they changed their practice in 2014 when it comes to the surveillance of allies and that they would cooperate with us and others to understand what happened," Solberg told news agency NTB.
Defence Minister Frank Bakke-Jensen said on Twitter his ministry had had a meeting with the US embassy in Oslo "where we made it clear that spying on allies is unacceptable and unnecessary".
There was no immediate comment from the US embassy.
Solberg said she had also spoken with her Danish counterpart, Mette Frederiksen, about the case on Thursday.
"I reiterated to her that we consider spying on close friends and allies as unacceptable and unnecessary," she said.
Danish state broadcaster DR reported on Sunday the NSA used Danish information cables to spy on senior officials in Sweden, Norway, France and Germany, including German Chancellor Angela Merkel.