British and American spooks are able to eavesdrop on several German telecoms networks, according to the news magazine Der Spiegel.
The so-called Treasure Map allows agents from the National Security Agency (NSA) and Government Communications Headquarters (GCHQ) to observe network traffic in what the magazine calls "Google Earth for the internet".
Thomas Tschersich, head of cybersecurity at Deutsche Telekom, told Der Spiegel: "Foreign secret services accessing on our network would be completely unacceptable.
"We investigate every indication of a possible manipulation."
Documents obtained by the German magazine from the NSA whistleblower Edward Snowden are said to show monitoring of networks belonging to Deutsche Telekom, Stellar, Netcologne and Cetel.
Previously the New York Times revealed that the Treasure Map programme had been described in an internal NSA presentation as "a near real-time, interactive map of the global internet".
It is said to collect Wi-Fi network and location data, and captures between 30 million to 50 million internet provider addresses every day.
Allegations that Americans were tapping the phones of German ministers including those belonging to the chancellor Angela Merkel caused outrage last October.
