The European Union has demanded that the United States explain a report in a German magazine that Washington is spying on the group, using strong language to confront its closest trading partner over its alleged surveillance activities.
EU High Representative Catherine Ashton said on Sunday that U.S. authorities were immediately contacted about a report in Der Spiegel magazine that the U.S. spy agency had tapped EU offices in Washington, Brussels and at the United Nations.
"As soon as we saw these reports, the European External Action Service made contact with the U.S. authorities in both Washington D.C. and Brussels to seek urgent clarification of the veracity of, and facts surrounding, these allegations," Ashton said in a statement.
"The U.S. authorities have told us they are checking on the accuracy of the information released yesterday and will come back to us as soon as possible," she said.
France also asked for an explanation.
"These acts, if confirmed, would be completely unacceptable," Foreign Minister Laurent Fabius said.
The U.S. government said it would respond through diplomatic channels.
"We will also discuss these issues bilaterally with EU member states," a spokesperson for the Director of National Intelligence said.
"While we are not going to comment publicly on specific alleged intelligence activities, as a matter of policy we have made clear that the United States gathers foreign intelligence of the type gathered by all nations."
The Guardian newspaper said in an article late on Sunday that the United States had also targeted non-European allies for spying.
Citing a September 2010 NSA document, the British newspaper said that "Along with traditional ideological adversaries and sensitive Middle Eastern countries, the list of targets includes the EU missions and the French, Italian and Greek embassies, as well as a number of other American allies, including Japan, Mexico, South Korea, India and Turkey."
Der Spiegel reported on Saturday that the National Security Agency bugged EU offices and gained access to EU internal computer networks, the latest revelation of alleged U.S. spying that has prompted outrage from EU politicians.
The magazine followed up on Sunday with a report that the U.S. agency taps half a billion phone calls, emails and text messages in Germany in a typical month, much more than any other European peer and similar to the data tapped in China or Iraq.
It also uses data from Internet hubs in south and west Germany that organize data traffic to Syria and Mali.
Revelations about the U.S. surveillance program, which was made public by fugitive former NSA contractor Edward Snowden, have raised a furor in the United States and abroad over the balance between privacy rights and national security.
The extent to which Washington's EU allies are being monitored emerged is a particular concern in Europe.
"If the media reports are correct, this brings to memory actions among enemies during the Cold War. It goes beyond any imagination that our friends in the United States view the Europeans as enemies," German Justice Minister Sabine Leutheusser-Schnarrenberger said.
"If it is true that EU representations in Brussels and Washington were indeed tapped by the American Secret Service, it can hardly be explained with the argument of fighting terrorism," she said in a statement.