LUXEMBOURG (AFP) - The European Union said on Friday it is concerned that a vast secret US intelligence gathering operation could affect the privacy of EU citizens.

"We have seen media reports about this," EU Home Affairs Commissioner Cecilia Malmstroem said.

"We are of course concerned about the possible consequences for EU citizens' privacy but it's far too early to draw any conclusions at the moment," Ms Malmstroem said after a meeting with her EU colleagues in Luxembourg. "We will be contacting our American counterparts to seek more information about this," she added.

The latest revelations show the US government organised a huge dragnet of Internet and phone data, with the FBI and National Security Agency (NSA) tapping servers of nine Internet giants - including Apple, Facebook, Microsoft, YouTube and Google..

Reports about the scope of the operation have deepened the controversy over the post-September 11 surveillance infrastructure set up by US intelligence agencies as a key element in the war against terror waged since the 2001 attacks on the United States.

US President Barack Obama staunchly defended the system Friday, saying the surveillance was legal and telling Americans "nobody is listening to your telephone calls."

Mr Obama also said there was a tradeoff to be made between national security and people's privacy although he conceded it was right that the exact balance between the two should be publicly debated.