Merkel rival demands halt of EU-US talks

He noted that the current government, run by Angela Merkel, is trying to cover up the scandal and that it makes no sense to negotiate on sensitive trade issues when the US can know at any point what the EU is discussing internally.

"We don't know if the Americans may be sitting under our desks with some technical devices," Steinbrueck said.

The Social-Democrat described the spying affair as detrimental to German companies which stand to lose their competitive advantage if the Americans are involved in "economic surveillance."

"Merkel is saying one thing about all this: Let's wait. I don't think a Chancellor should wait when civil liberties are at stake," Steinbrueck said.

Merkel has so far maintained she has no evidence the US violated German law and that her team is now negotiating a bilateral no-spying pact with America.

But Steinbrueck says the pact is lipservice to German concerns and will not prevent the US from carrying on with spying activities.

Meanwhile, documents leaked to Der Spiegel by Edward Snowden, the former US security contractor who has fled to Russia, reveal that US secret services also bugged the offices of the United Nations in New York, along with EU offices in the city.

Last summer, the National Security Agency (NSA) cracked the encryption of the videoconference system in the UN headquarters - an illegal activity since the US has signed an agreement with the UN not to carry out any spying on its premises, Der Spiegel reports.

The documents obtained by the German magazine also show that over 80 US embassies and consulates abroad, including the US consulate in Frankfurt, are involved in a spying programme called Special Collection Service, which is carried out without the host country knowing anything about it.

The existence of this programme has to be kept secret, according to the Snowden documents. Else it would "bring considerable damage to relations with the host country," Spiegel quotes from one document.