"We swiftly sent a request to our American partners asking for an immediate and comprehensive clarification," Steffen Seibert, a German government spokesman said in a statement on Wednesday.
He added that Merkel had made clear to Obama that if the information proved true it would be "completely unacceptable" and represent a "grave breach of trust".
Merkel's spokesman Steffen Seibert said that the chancellor had made clear that "she unambiguously condemns such practices if they prove to be true and considers them completely unacceptable. They would constitute a grave breach of trust. Such practices would have to be stopped immediately."
The White House later said Obama had assured Merkel that the US was not monitoring her communications. White House spokesman Jay Carney confirmed Obama and Merkel had spoken by phone on Wednesday.
Carney said: "The United States is not monitoring and will not monitor the communications of the chancellor."
WHEN WILL THEY LEAVE POOR BARACK ALONE................