Germany summons US ambassador over claims
Germany summoned the US ambassador in Berlin over claims that the US monitored German Chancellor Angela Merkel's mobile phone.
Foreign Minister Guido Westerwelle will meet US envoy John Emerson later in what is seen as an unusual step between close allies.
Merkel has demanded a "complete explanation" of the claims, which are threatening to overshadow an EU summit.
She discussed the issue with US President Barack Obama on Wednesday.
President Obama told Merkel the US was not monitoring her calls and would not in future, the White House said.
However, it left open the question of whether calls had been listened to in the past.
On Monday, France summoned the US ambassador over reports in Le Monde newspaper that the US National Security Agency (NSA) had spied on millions of French phone calls. A day later, Le Monde reported that the NSA had spied on French diplomats in Washington and at the UN.
French President Francois Hollande had already called for the issue to be put on the agenda of the summit, where EU leaders are due to discuss Europe's digital economy, economic recovery and immigration.
Other leaders are also likely to want further clarification from Washington over the activities of its NSA in Europe, says BBC Europe Editor Gavin Hewitt.
"It's really not on for friends to spy on each other," said Chancellor Merkel as she arrived at the EU summit in Brussels.
The German government has not said how it received the tip about the alleged US spying. But news magazine Der Spiegel, which has published stories based on material from former CIA contractor Edward Snowden, said the information had come from its investigations.
State-monitoring of phone calls has a particular resonance in Germany - Merkel herself grew up in East Germany, where phone-tapping was pervasive.
Gunther Krichbaum, the chairman of the European affairs committee in Germany's Bundestag, told the BBC that "if it turns out to be true this... is a real scandal".
Krichbaum said he was convinced that he and his colleagues would "not go ahead" with negotiations over a major trade treaty with the US before finding out what had happened.
White House spokesman Jay Carney said the US "is not monitoring and will not monitor the communications of the chancellor".
Germany's press echoed a sense of outrage, with a front-page commentary Sueddeutscher Zeitung - one of the country's most respected papers - referring to the "biggest possible affront".