LONDON -- European officials reacted angrily on 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 newsmagazine Der Spiegel, which reported that American agencies had monitored the offices of the European Union 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 E.U.-U.S. relations," he said, adding that he wanted a "full clarification" and would demand "further information speedily from the U.S. authorities."
Viviane Reding, the European Union'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 European Union diplomatic offices in downtown Washington and tapped into its computer network.
"In this way, the Americans were able to access discussions in E.U. 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.
Late Sunday, The Guardian, the British newspaper and global Web site that during the past week published a string of articles about classified N.S.A. programs, reported that American intelligence officials had been spying on the European Union mission in New York as well.
The latest release of top secret N.S.A. documents suggested that the spying against European Union was intended to gather information about policy disagreements and other disagreements between member states, The Guardian said. Along with traditional adversaries and Middle Eastern countries, the report said the list included the French, Italian and Greek embassies, as well as several other American allies, including Japan, Mexico, South Korea, India and Turkey.
Der Spiegel also suggested that eavesdropping took place in Brussels, in the Justus Lipsius Building, where representatives of European Union members have their offices.
Mr. 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 Mr. Snowden and his cause, said Sunday that the revelations would continue. "Look, there is no stopping the publishing process at this stage," Mr. Assange said on the ABC News program "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 Mr. Snowden can't be pressured by any state to stop the publication process."
Mr. Snowden's fate remained murky on Sunday. Ecuador, which has been thought to be his preferred destination, said his next move depended on Russia.
''It's up to the Russian authorities if he can leave the Moscow airport for an Ecuadorean Embassy,'' President Rafael Correa of Ecuador told Reuters. He confirmed that his government could not begin considering an asylum request until Mr. Snowden reached Ecuador or an Ecuadorean embassy.
Mr. Snowden 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.
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 that the government had urgently demanded an explanation from the American 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." Mr. Asselborn's spokesman confirmed the comment.
The most vocal criticism came from Germany, where privacy issues are a matter of significance.
"If the media reports are accurate, then this recalls the methods used by enemies during the cold war," the justice minister, Sabine Leutheusser-Schnarrenberger, said. "It is beyond comprehension that our friends in the United States see Europeans as enemies," she said, according to The Associated Press.
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 U.S.A. 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.
Talks to hammer out a trans-Atlantic trade agreement are supposed to begin in the coming weeks, with a target date to complete them by November 2014.
Both sides have been thought to have considerable incentive to push through an agreement to help the economies on both sides of the Atlantic and create thousands of jobs.
But any new trade deal would require approval by the European Parliament and ratification by the United States Congress.
This article originally appeared in The New York Times.