BERLIN: The United States taps half a billion phone calls, emails and text messages in Germany in a typical month and has classed its biggest European ally as a target similar to China, according to secret US documents quoted by a German newsmagazine.

Moreover the European Union said on Sunday said it has questioned US authorities about alleged US spying on EU offices and was waiting for Washington's response.

“We have immediately been in contact with the US authorities in Washington DC and in Brussels and have confronted them with the press reports, “ the European Commission said in a statement.

“They have told us they are checking on the accuracy of the information released yesterday and will come back to us,” it said referring to a report on the spying claims by German weekly Der Spiegel.

The revelations of alleged US surveillance programmes based on documents taken by fugitive former National Security Agency contractor Edward Snowden have raised a political furore in the United States and abroad over the balance between privacy rights and national security.

Exposing the latest details in a string of reputed spying programmes, Der Spiegel quoted from an internal NSA document which it said its reporters had seen.

The document Spiegel cited showed that the United States categorised Germany as a “third-class” partner and that surveillance there was stronger than in any other EU country, similar in extent to China, Iraq or Saudi-Arabia.

“We can attack the signals of most foreign third-class partners, and we do it too,” Der Spiegel quoted a passage in the NSA document as saying.

It said the document showed that the NSA monitored phone calls, text messages, emails and internet chat contributions and has saved the metadata, that is the connections and not the content, at its headquarters.

On an average day, the NSA monitored about 20 million German phone connections and 10 million internet data sets, rising to 60 million phone connections on busy days, the report said.

While it had been known from disclosures by Snowden that the United States tapped data in Germany, the extent was previously unclear.

News of the US cyber-espionage programme Prism and the British equivalent Tempora have outraged Germans, who are highly sensitive to government monitoring having lived through the Stasi secret police in the former communist East Germany and with lingering memories of the Gestapo of Hitler's Nazi regime.

A Spiegel report on Saturday that the NSA had spied on European Union offices caused outrage among EU policymakers, with some even calling for a suspension to talks for a free trade agreement between Washington and the EU.

In France, Der Spiegel reported, the United States taps about 2 million connection data a day.

Only Canada, Australia, Britain and New Zealand were explicitly exempted from spy attacks.

Snowden, a US citizen, fled the United States to Hong Kong in May, a few weeks before the publication in the Guardian and the Washington Post of details he provided about secret US government surveillance of internet and phone traffic.

He has been holed up in a Moscow airport transit area for a week after US authorities revoked his passport.

The leftist government of Ecuador is reviewing his request for asylum.