Those targeted reportedly included German Chancellor Angela Merkel, then German Foreign Minister Frank-Walter Steinmeier and former German opposition leader Peer Steinbrück.
The revelation came to light from a 2014 internal investigation by the Danish Defense Intelligence Service (FE) on its cooperation with US National Security Agency (NSA). DR spoke to anonymous intelligence figures privy to that report.
They reportedly collaborated between 2012 and 2014.
Denmark helped US spy on Germany
How has Norway reacted?
Norwegian Prime Minister Erna Solberg told Norwegian news agency NTB that "the Americans have clearly said that they changed their practice in 2014 when it comes to monitoring allies, and that they will work with us and others to clarify what has happened."
"We have today met with the US embassy in Oslo to follow up on this invitation," Solberg told the NTB.
On Thursday, she met with the Danish prime minister, where she said that espionage against allies is "unacceptable and unnecessary," public broadcaster NRK reported.
Defense Minister Frank Bakke-Jensen met with officials in the US embassy to convey that same message, his ministry said in a post on Twitter.