Angela Merkel has called President Barack Obama after receiving information that the US may have spied on her mobile phone.
A spokesman for Angela Merkel said the German Chancellor “views such practices… as completely unacceptable”.
Angela Merkel has called on US officials to clarify the extent of their surveillance in Germany.
The White House said President Barack Obama had told Chancellor Merkel the US was not snooping on her communications.
“The United States is not monitoring and will not monitor the communications of the chancellor,” White House spokesman Jay Carney said.
Jay Carney told reporters that Washington was examining concerns from Germany as well as France and other American allies over US intelligence practices.
The call comes a day after US intelligence chief James Clapper denied reports that American spies had recorded data from 70 million phone calls in France in a single 30-day period.
James Clapper said a report in Le Monde newspaper contained “misleading information”.
The German government would not elaborate over how it gained its information about alleged US spying on its leader’s communications.
German news magazine Der Spiegel, which has published stories based on material from NSA leaker Edward Snowden, said the information had come from its investigations.
Berlin demanded “an immediate and comprehensive explanation” from Washington about what it said “would be a serious breach of trust”.
“Among close friends and partners, as the Federal Republic of Germany and the US have been for decades, there should be no such monitoring of the communications of a head of government,” the statement.
The statement said that Angela Merkel had told Barack Obama: “Such practices must be prevented immediately.”
The US has also seen other allies angry over spying concerns.
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