President Barack Obama spoke with an angry Chancellor Angela Merkel of Germany on Wednesday after a news report said the National Security Agency (NSA) had tapped into her cell phone.

The controversy marked the second time this week that Obama had to assuage an upset European ally over NSA spying activities in their country.

Merkel called Obama after the German publication Der Spiegel discovered the NSA had eavesdropped on the German leader’s cell phone calls. The account was based on materials provided to Der Spiegel by NSA whistleblower Edward Snowden.

Prior to publishing the story, the newsmagazine shared its NSA data with German intelligence officials who reviewed the information and concluded it was likely that Merkel’s phone had been tapped by the U.S. spy agency.

During their phone call, Obama reportedly told Merkel that the U.S. was not listening in on her phone conversations.

An avid cell phone user, Merkel told Obama that she “unequivocally disapproves of such practices and sees them as completely unacceptable,” her spokesman, Steffen Seibert, said in a statement, adding that any monitoring “would be a grave breach of trust.”

When reporters subsequently asked White House press secretary Jay Carney if the NSA had previously monitored Merkel’s calls, he responded that he wasn’t able to answer that question.

The German government also complained that the U.S. has not responded to their questions, posed several months ago, about the level of NSA spying against Germany.

The outrage in Berlin came only days after President François Hollande of France had called the White House to confront Obama over news published in the French newspaper Le Monde that the NSA had intercepted the phone calls and text messages of millions of French people.

Using information disclosed by Snowden, Le Monde said that more than 70 million French phone calls were recorded in just one 30-day period late last year by the NSA.

Revelations and subsequent outrage have abounded this year, all stemming from the leaked Snowden documents, relating to NSA surveillance on numerous countries, including U.S. allies. It was reported that the agency has gathered data on telephone calls and emails from Brazil, Colombia, Venezuela and Mexico, including those from the offices of the presidents of Mexico and Brazil.

At a news conference in July, Merkel said that she fully understood America’s alarm following the September 11, 2001, terrorist attacks. But “the aim does not justify the means,” she insisted. “Not everything which is technically doable should be done. The question of relative means must always be answered: What relation is there between the danger and the means we choose, also and especially with regard to preserving the basic rights contained in our Basic Law?”

-Noel Brinkerhoff, Danny Biederman

To Learn More:

German Leader Calls Obama About Alleged Cellphone Tapping (by Michael Birnbaum and Ellen Nakashima, Washington Post)

Berlin Complains: Did US Tap Chancellor Merkel's Mobile Phone? (by Jacob Appelbaum, Holger Stark, Marcel Rosenbach and Jörg Schindler, Der Spiegel)

Angela Merkel's Call to Obama: Are You Bugging My Mobile Phone? (by Ian Traynor, Philip Oltermann, and Paul Lewis; The Guardian)

Anger Growing Among Allies Over U.S. Surveillance (by Alison Smale, New York Times)

German Spy Agency Supplies NSA with Daily Trove of Surveillance Data (by Danny Biederman and Noel Brinkerhoff, AllGov)

Concerned U.S. Allies Want Privacy Guarantees in Wake of NSA Revelations (by Noel Brinkerhoff, AllGov)