Senior European officials expressed concern Sunday at reports that U.S. intelligence agents bugged EU offices on both sides of the Atlantic, with some leftist lawmakers calling for concrete sanctions against Washington.

The president of the European Parliament, Martin Schulz, said he was “deeply worried and shocked about the allegations of U.S. authorities spying on EU offices” made in a report published Sunday by German news weekly Der Spiegel.

The magazine said the surveillance was carried out by the U.S. National Security Agency, which has recently been the subject of leaks claiming it scanned vast amounts of foreign Internet traffic. The U.S. government has defended its efforts to intercept electronic communications overseas by arguing that this has helped prevent terror attacks at home and abroad.

Schulz said that if the allegations that the NSA bugged European Union offices were confirmed “it would be an extremely serious matter which will have a severe impact on EU-US relations.”

Green Party leaders in the European Parliament, Rebecca Harms and Daniel Cohn-Bendit, called for an immediate investigation into the claims and suggested that recently launched negotiations on a trans-Atlantic trade treaty should be put on hold.

They also called for existing U.S.-EU agreements on the exchange of bank transfer and passenger record information to be canceled. Both programs have been labeled as unwarranted infringements of citizens’ privacy by left-wing and libertarian lawmakers in Europe.

In Germany, where criticism of the NSA’s surveillance programs has been particularly vocal, a senior government official accused the United States on Sunday of using Cold War methods against its allies by targeting EU offices in Washington, New York and Brussels.

“If the media reports are accurate, then this recalls the methods used by enemies during the Cold War,” German Justice Minister Sabine Leutheusser-Schnarrenberger. “It is beyond comprehension that our friends in the United States see Europeans as enemies.”

Leutheusser-Schnarrenberger called for an “immediate and comprehensive” response from the U.S. government to the claims in the Spiegel report, which cited classified U.S. documents taken by former NSA contractor Edward Snowden that the magazine said it had partly seen.

Spokespeople for the NSA and the office for the national intelligence director in Washington did not immediately respond to requests for comment Sunday.

According to Der Spiegel, the NSA planted bugs in the EU’s diplomatic offices in Washington and infiltrated the building’s computer network. Similar measures were taken at the EU’s mission to the United Nations in New York, the magazine said.

Der Spiegel didn’t publish the alleged NSA documents it cited nor say how it obtained access to them. But one of the report’s authors is Laura Poitras, an award-winning documentary filmmaker who interviewed Snowden while he was holed up in Hong Kong.

The U.S. has been trying to track down Snowden, who is believed to currently be at Moscow’s main airport with plans to travel to Ecuador to seek asylum.

The magazine also didn’t specify how it learned of the NSA’s alleged eavesdropping efforts at a key EU office in Brussels. There, the NSA used secure facilities at NATO headquarters nearby to dial into telephone maintenance systems that would have allowed it to intercept senior EU officials’ calls and Internet traffic, the Spiegel report said.

Also Sunday, German federal prosecutors said they were examining whether the reported U.S. electronic surveillance programs broke German laws. In a statement, the Federal Prosecutors’ Office said it was probing the claims so as to “achieve a reliable factual basis” before considering whether a formal investigation was warranted.

It said private citizens were likely to file criminal complaints on the matter, but didn’t comment on the possible legal merits of such complaints.

Der Spiegel reported that at least one such complaint was lodged with prosecutors in the state of Hesse last week.

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Frank Jordans can be reached at http://www.twitter.com/wirereporter . Associated Press Writer Raf Casert contributed to this report from Brussels.