PARIS - French President Emmanuel Macron said on Monday that all must be clarified concerning reports that the United States intelligence agency had used the Danish infrastructure to spy on senior European officials, including German Chancellor Angela Merkel.

This "is unacceptable between allies, even less between allies and European partners", Macron was quoted by French daily Le Monde following a French-German council of ministers. He urged "all the clarity".

Denmark's national broadcaster DR News reported on Sunday that Danish Defense Intelligence Service (FE) has given the US National Security Agency (NSA) open internet access to spy on senior politicians of neighboring countries, including Merkel.

DR News, in collaboration with Swedish, Norwegian, German and French media, found out some "startling conclusions" in a secret internal investigation on the FE dubbed as "Operation Dunhammer," which was concluded in May 2015.

A significant conclusion in the Dunhammer report, according to DR News, is that the NSA has purposefully obtained data and thus been able to clandestinely spy on targeted heads of state, as well as neighboring Scandinavian leaders, top politicians, and high-ranking officials in Germany, Sweden, Norway, and France.

Earlier in the day, France's Secretary of State for European Affairs Clement Beaune told Franceinfo radio that what has been found by the media investigation "is extremely serious".

"We must verify these facts and denounce them if it is true," he said.