Germany has summoned the US ambassador to Berlin to demand a “complete explanation”, over claims that US intelligence agencies spied on telephone calls made by the country’s Chancellor Angela Merkel.

American Ambassador John Emerson will meet German Foreign minister Guido Westerwelle later today (Thursday), as EU leaders meet for a two-day summit in Brussels. Those talks are likely to be overshadowed by a swirl of controversy over US spy agencies’ intelligence gathering techniques, including allegations that American spies snooped on foreign diplomats and government officials.

Following the initial allegations yesterday, Merkel’s spokesman released a statement saying that the Chancellor “views such practices… as completely unacceptable.”

“Among close friends and partners, as the Federal Republic of Germany and the US have been for decades, there should be no such monitoring of the communications of a head of government,” the statement continued.

White House spokesperson Jay Carney denied that intelligence agencies were listening in on the German leader’s private calls, insisting that “The United States is not monitoring and will not monitor the communications of the chancellor.”

However, the carefully-worded statement did not rule out the possibility that intelligence agencies had spied on the German leader in the past.