The US spied on top politicians in Europe, including German Chancellor Angela Merkel, from 2012 to 2014 with the help of Danish intelligence, Danish and European media reported on Sunday.

Danish public broadcaster Danmarks Radio (DR) said the US National Security Agency (NSA) had eavesdropped on Danish internet cables to spy on top politicians and high-ranking officials in Germany, Sweden, Norway and France.

The NSA had taken advantage of a surveillance collaboration with Denmark's military intelligence unit FE to do so, it said.

Danish Defence Minister Trine Bramsen declined to comment on "speculation" about intelligence matters in the media.

"I can more generally say that this government has the same attitude as the former Prime Minister expressed in 2013 and 2014 - systematic wiretapping of close allies is unacceptable," Bramsen told Reuters in a statement.

In Washington, the NSA and the Office of the Director of National Intelligence (DNI) declined to comment. A spokesperson for the Danish Defence Intelligence Service also declined to comment.

Denmark, a close ally of the United States, hosts several key landing stations for subsea internet cables to and from Sweden, Norway, Germany, Holland and Britain.

The alleged set-up, said in the report to have been codenamed "Operation Dunhammer", allowed the NSA to obtain data using the telephone numbers of politicians as search parameters, according to DR.