The Danish government has distanced itself from certain spying practices, after reports emerged that Denmark supported the United States' wiretapping of German Chancellor Angela Merkel and other high-ranking politicians about a decade ago.
"Systematic wiretapping of close allies is unacceptable," Defence Minister Trine Bramsen said on Monday.
In Berlin, government spokesperson Steffen Seibert said: "We are in concordance with her general assessment."
He added the German government was in touch with all relevant countries and international bodies for clarification on the matter.
Investigative journalists from Danish broadcaster DR, together with German media outlets like NDR, WDR and the Sueddeutsche Zeitung, reported on Sunday that the US National Security Agency (NSA) had spied on European politicians with the help of Denmark.
The research was based on anonymous sources and an internal analysis of the Danish military intelligence service FE from 2012 and 2014.
Aside from Merkel, other German politicians - such as President Frank-Walter Steinmeier as well as leaders in France, Sweden and Norway - were targeted.
Their phones were allegedly wiretapped with the help of software created by FE.
According to DR, the alleged set-up between the United States and Denmark was codenamed "Operation Dunhammer".
The investigation revealed for the first time the extent of alleged military intelligence collaboration between Denmark and the US, and expanded the list of names of the politicians targeted.
Former NSA contractor Edward Snowden, who revealed details of the secret US eavesdropping programs in 2013, reacted to the DR report with a sarcastic tweet in Danish: "Oh, why didn't anyone warn us?"
Bramsen said she could not comment on speculation about possible intelligence activity.
FE also did not comment on the allegations.