German Chancellor Angela Merkel complained to President Barack Obama on Wednesday after learning that U.S. intelligence may have targeted her mobile phone, and said that would be “a serious breach of trust” if confirmed, her government announced.

The White House denied that the U.S. is listening in on Merkel’s phone calls.

The German government said it responded after receiving “information that the chancellor’s cellphone may be monitored” by U.S. intelligence. It wouldn’t elaborate but German news magazine Der Spiegel, which has published material from NSA leaker Edward Snowden, said its research triggered the response.

Merkel spokesman Steffen Seibert said in a statement the chancellor made clear to Obama in a phone call that “she views such practices, if the indications are confirmed … as completely unacceptable.”

Merkel said among close partners such as Germany and the U.S., “there must not be such surveillance of a head of government’s communication,” Seibert added. “That would be a serious breach of trust. Such practices must be stopped immediately.”

In Washington, White House spokesman Jay Carney said “the United States is not monitoring and will not monitor the communications of the chancellor.”

Merkel raised concerns over electronic eavesdropping issue when Obama visited Germany in June, has demanded answers from the U.S. government and backed calls for greater European data protection. However, Wednesday’s statement was much more sharply worded and appeared to reflect frustration over the answers provided so far by the U.S. government.

Merkel called for U.S. authorities to clarify the extent of surveillance in Germany and to provide answers to “questions that the German government asked months ago,” Seibert said.

(AP)