Merkel makes irate call to Obama over phone-tapping

German chancellor Angela Merkel has complained to US President Barack Obama after learning that the National Security Agency have targeted her mobile phone in its now infamous global surveillance programme.

Merkel told Obama that this would be "a serious breach of trust" if confirmed.

The White House has denied that US agencies are listening in on Merkel's phone calls now; but was strangely quiet on the past.

"The president assured the chancellor that the United States is not monitoring and will not monitor the communications of the chancellor," White House spokesman Jay Carney said. "The United States greatly values our close cooperation with Germany on a broad range of shared security challenges."

However, Carney did not specifically say that that US had never monitored or obtained Merkel's communications.

The German government said it responded after receiving "information that the chancellor's cellphone may be monitored" by US intelligence. It wouldn't elaborate, but Germany's widely-respected 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 US, "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."

Carney said the US is examining Germany's concerns as part of an ongoing review of how the US gathers intelligence.

The White House has cited that review in responding to similar spying concerns from France, Brazil and other countries.

As details of the NSA spying programmes have become public, citizens, activists and politicians in countries from Latin America to Europe have lined up to express shock and outrage at the scope of Washington's spying.

Merkel had previously raised concerns over the electronic eavesdropping issue when Obama visited Germany in June. The head of Europe's leading economy has demanded answers from the US government and backed calls for greater European data protection.

Wednesday's statement, however, was much more sharply worded and appeared to reflect frustration over the answers provided so far by the US government.

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