New claims have emerged over the extent of United States intelligence agencies' monitoring of the mobile phone of Chancellor Angela Merkel.
The allegations were made as German secret service officials were preparing to travel to Washington to seek explanations into the alleged surveillance of the Chancellor.
A report in Der Spiegel said the Chancellor's mobile number had been listed by the National Security Agency's Special Collection Service (SCS) since 2002 and might have been monitored for more than 10 years.
It was still on the list - marked as "GE Chancellor Merkel" - weeks before President Barack Obama visited Berlin in June.
In an SCS document cited by the magazine, the agency said it had a "not legally registered spying branch" in the US Embassy in Berlin, the exposure of which would lead to "grave damage for the relations of the United States to another Government".
From there, NSA and CIA staff were tapping communication in Berlin's government district with high-tech surveillance. Quoting a secret document from 2010, Der Spiegel said such branches existed in about 80 locations around the world, including Paris, Madrid, Rome, Prague, Geneva and Frankfurt.
Merkel's spokesman and the White House declined to comment.
The nature of the monitoring of Merkel's mobile phone was not clear from the files, Der Spiegel said. It might be that the Chancellor's conversations were recorded, or her contacts were simply assessed.
Bild am Sonntag added further details, yesterday reporting that the NSA spied on Merkel's predecessor, Gerhard Schroeder, after President George W. Bush launched a spying programme in 2002.
The newspaper suggested a key reason was Schroeder's refusal to support the Iraq War. Merkel took office in 2005.
The Frankfurter Allgemeine Sonntagszeitung reported that Obama had told Merkel during a phone conversation last week that he had not known of the spying. But Bild am Sonntag cited an unnamed NSA official who said the President ordered the bugging to be escalated.
The newspaper reported that Obama knew the NSA had been spying on Merkel's mobile phone since at least 2010, when agency chief Keith Alexander told him about the operation.
Bild am Sonntag reported that the NSA listened to her mobile phone, and another phone. It said the contents of text messages and phone calls were reported directly to the White House.
Ahead of the latest claims, the German Government's deputy spokesman, Georg Streiter, said a high-level delegation was heading to the White House and NSA to "push forward" investigations into earlier surveillance allegations. The delegation will include senior officials from the German secret service, according to German media reports.
Several thousand people marched to the US Capitol in Washington yesterday to protest against the NSA's spying programme and to demand a limit to the surveillance. Some of them held banners in support of Edward Snowden, the former CIA contractor who revealed the extent of the NSA's activities.
Germany and Brazil are spearheading efforts at the UN to protect the privacy of electronic communications. Diplomats from the two countries, which have both been targeted by the NSA, are leading efforts by a coalition of nations to draft a UN General Assembly resolution calling for the right to privacy on the internet.
Although non-binding, the resolution would be one of the strongest condemnations of US snooping to date.