The US National Security Agency spied on internet traffic in allied nations including the Netherlands from an island in Denmark, a Danish broadcaster has claimed.

American agents were able to use a cable network set up in 2008 in conjunction with the Danish secret service Forsvarets Efterretningstjeneste (FE) to tap into internet traffic in France, Germany, the Netherlands, Sweden and Norway.

A whistleblower within the Danish agency passed documents to Danish broadcaster DR after his attempts to raise the issue internally fell on deaf ears, NRC reported. An external inquiry in August prompted the departure of the head of the FE.

It is not clear which internet users in the Netherlands were monitored or what the purpose was, according to NRC. The data obtained was stored on a Danish island which both FE and NRC agents had access to.

The NSA used a spyware program called Xkeyscore to sweep up internet data including browser history, email exchanges, documents and chat sessions from large numbers of users.