LONDON — European officials reacted angrily Sunday to a report that the United States had been spying on its European Union allies, saying the claims could threaten talks with Washington on an important trade agreement.
The latest allegations surfaced in the online edition of the German news magazine Der Spiegel, which reported that US agencies had monitored the offices of the EU in New York and Washington. Der Spiegel said information about the spying appeared in documents obtained by Edward J. Snowden, the former American intelligence contractor, and seen in part by the magazine.
The president of the European Parliament, Martin Schulz, said in a statement that he was “deeply worried and shocked.”
“If the allegations prove to be true, it would be an extremely serious matter which will have a severe impact on EU-US relations,” he said, adding that he wanted a “full clarification” and would demand “further information speedily from the US authorities.”
Viviane Reding, the EU’s commissioner for justice, responding to a question at a meeting in Esch-sur-Alzette, Luxembourg, said that “partners do not spy on each other.”
“We cannot negotiate over a big trans-Atlantic market if there is the slightest doubt that our partners are carrying out spying activities on the offices of our negotiators,” she said. “The American authorities should eliminate any such doubt swiftly.”
According to Der Spiegel, the National Security Agency installed listening devices in EU diplomatic offices in downtown Washington and tapped into its computer network.
‘If the allegations prove to be true, it . . . will have a severe impact on EU-US relations.’ — Martin Schulz, President of the European Parliament
“In this way, the Americans were able to access discussions in EU rooms as well as e-mails and internal documents on computers,” the article said. It said that the bloc’s representative offices at the United Nations in New York were similarly targeted.
The news magazine also suggested that eavesdropping took place in Brussels, in the Justus Lipsius Building, where representatives of EU members have their offices.
Snowden, who last month revealed details about American surveillance programs, fled to Hong Kong shortly before his revelations became public, then moved on to Moscow, where he is in diplomatic limbo at an airport there.
Julian Assange, whose antisecrecy organization, WikiLeaks, is supporting Snowden and his cause, said Sunday the revelations would continue.
“Look, there is no stopping the publishing process at this stage,” Assange said on ABC’s “This Week” in an interview from the Ecuadorean Embassy in London, where he has been granted asylum. “Great care has been taken to make sure that Snowden can’t be pressured by any state to stop the publication process.”
Snowden’s fate remained murky on Sunday. He has been in a transit area at Sheremetyevo Airport near Moscow since June 23. He is believed to be trying to negotiate travel arrangements to Ecuador, Venezuela, or elsewhere.
Michael Hayden, the former director of the CIA and National Security Agency, said Sunday the US government should release more information about its secretive surveillance programs to reassure Americans that their privacy rights are being protected.
In an interview on CBS’s “Face the Nation,’’ Hayden said he believes people would be more comfortable with the programs that gather phone and Internet records from around the world if they knew more about how the process is carried out and why.
Hayden also defended a secret court that approves government requests to gather the records. Critics say the Foreign Intelligence Surveillance Court has served as a rubber stamp to the requests instead of challenging government attorneys on whether the information is needed or gathered properly.
To longtime European diplomats, the new spying claims may come as little surprise. There were reports in 2003 that foreign intelligence agencies had planted listening devices in the Justus Lipsius Building, and a number of intelligence officers are thought to be among the thousands of diplomats working in Brussels.
By listening in on the discussions in Brussels — mainly on technical issues, though they could be crucial in talks about a trade accord — officials can gain advantage by knowing their counterparts’ negotiating positions.
Foreign Minister Laurent Fabius of France said Sunday the government had urgently demanded an explanation from US authorities. Should the report of spying be confirmed, he said in a statement, it would be “completely unacceptable.” And Jean Asselborn, the foreign minister of Luxembourg, told Der Spiegel that “if these reports are true, it’s disgusting.”
The most vocal criticism came from Germany, where privacy issues are a matter of significance. Birgit Sippel, a Social Democrat and member of a European Parliament committee on civil liberties, said on Twitter that she would like “to suspend upcoming negotiations with the USA and to review existing agreements.”
Rebecca Harms, a president of the Greens Party in the European Parliament, called for a special committee to investigate the claims and the possible cancellation of existing agreements between the bloc and the United States on bank transaction information and passenger record data.
“The last few days have shown how urgently we need an international agreement on data protection,” she said.