Germany today summoned the US ambassador over claims that Chancellor Angela Merkel's mobile phone may have been monitored for several years by American intelligence services.
Foreign Minister Guido Westerwelle will meet US envoy John Emerson later in what is seen as an unusual step between close allies.
Meanwhile, Chancellor Merkel today said that such conduct between friends was unacceptable.
"Spying between friends, that's just not done," Merkel said as she reached Brussels for a two-day European Union summit where the growing spy scandal has hijacked the agenda.
"I said that to US President Barack Obama when he came to Berlin and again on the phone (Wednesday). We need trust between partners and such trust needs to be re-established," Merkel said.
Merkel said she told Obama that there needs to be trust among allies and partners and "such trust now has to be built anew."
Germany yesterday demanded an explanation from the US over the claims and asked the US authorities with great urgency to provide "speedy and detailed clarification", a government spokesman said.
Germany's external intelligence agency BND and the Federal Office for Security in Information Technology received indications for the suspected surveillance of the chancellor during an investigation, according to media reports.
Merkel called US president Barack Obama yesterday that between Germany and the US, which are close friends and partners for decades, monitoring of a head of government should never happen.
"If that happens, it will be a grave breach of confidence and such practises must be stopped immediately," she said.
The chancellor expressed the hope that the US authorities would provide clarification on the full extent of the surveillance operations against Germany, including answering the questions raised by the German government several months ago, the statement said.
As a close NATO partner of the US, Germany expects that in the future, there will be a clear mutually agreed basis for the operation of intelligence services and their cooperation.
The opposition Left party demanded chancellor Merkel to inform parliament about the indications for a possible monitoring of her mobile phone.
If the suspicions were proved true, "it will be the worst breach of confidence among friends", co-chairperson of the party Katja Kipping said in an interview.
