Berlin, Jun 30 (IANS): The US National Security Agency (NSA) not only monitors the communications of European citizens, but it also has an eavesdropping programme targeting offices of the European Union (EU), a media report said.

German magazine Der Spiegel cited confidential documents it obtained from whistleblower Edward Snowden, Xinhua reported.

Snowden, who worked for the CIA, fled to Hong Kong last month and revealed an NSA-operated classified surveillance project code-named "PRISM", which can trace worldwide e-mails and phone calls.

A document dated September 2010 and classified as "strictly confidential" showed how the NSA spied on the EU's diplomatic mission in Washington, the magazine said.

Eavesdropping bugs were installed in the EU buildings and the internal computer network was infiltrated, through which the American intelligence can get access to EU meetings, e-mails and internal documents, it said.

The EU representation at the UN office in New York was also under similar surveillance, the magazine said.

In addition, the US intelligence also eavesdrops and monitors the Justus Lipsius building, the headquarters of the Council of the European Union, it said.

Meanwhile, the EU has warned the Obama administration of "grave adverse consequences" to the rights of the European citizens from the spy scheme and demanded "swift and concrete" answers.