Germany’s Federal Prosecutor’s office said it was preparing to bring charges against British and US intelligence today amid fresh allegations that the services spied far more extensively than thought on German phone and internet traffic and bugged European Union offices in America.

A report alleging a major and continuous US National Security Agency spying operation in Germany was published by Der Spiegel magazine today, prompting outrage from Berlin MPs still reeling from reports about extensive British surveillance in their country. The German Justice Minister, Sabine Leutheusser-Schnarrenburger, demanded an immediate explanation and said the behaviour of the intelligence services was “reminiscent of the actions against enemies during the Cold War”. “It defies belief that our friends in the US see the Europeans as their enemies,” she said.

The leak, which Der Spiegel said came from fugitive ex-CIA analyst Edward Snowden, claimed that the NSA tapped into half a billion German phone calls, emails and SMS messages each month. Reports last week revealed extensive tapping of German phone and internet traffic by British intelligence under its so-called Tempora programme. The information was said to be shared with the NSA.

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A spokesman for the Federal Prosecutor said the office was preparing to bring charges against “persons unknown” in relation to the reports.

There was also widespread and mounting anger at official European Union level yesterday following disclosures that the NSA had spied on EU computer networks at its offices in New York and Washington and that it had also bugged the premises. Martin Schulz, head of the European Parliament, demanded “full clarification” from the US and said that if the disclosures proved true they would have a severe impact on US-EU ties.

Today it also emerged that the UK Government had invited German MPs and justice officials to attend a video conference at British Embassy in Berlin tomorrow during which the issue of spying would be addressed.

Der Spiegel said the NSA’s German phone and internet surveillance operation was the biggest in the EU. On 7 January 2013 it tapped into some 60 million German phone calls in a single day. The magazine said that Canada, Australia, Britain and New Zealand were exempt from NSA surveillance but Germany was regarded as a country open for “spy attacks”.