SAN JOSE - US President Barack Obama on Friday forcefully defended revelations that the National Security Agency is collecting phone records and electronic communications, saying that Congress was fully briefed and the programmes are limited in scope.

“The programs are secret in the sense that they are classified. They are not secret, in that every member of Congress has been briefed,” he said during a speech in San Jose, California. “These are programs that have been authored by large bipartisan majorities repeatedly since 2006.”

“Your duly elected representatives have consistently been informed,” he said.

Obama said the programmes were “trade-offs” designed to strike a balance between privacy concerns and keeping Americans safe from terrorist attacks.  “Nobody is listening to your telephone calls. That’s not what this program is about,” Obama told reporters during a visit to California’s Silicon Valley.

News outlets revealed this week that vast spying programs began under President George W Bush and have continued under Obama.

The Guardian reported Wednesday that the National Security Agency had obtained a court order to collect phone records from Verizon Wireless customers, while The Washington Post reported Thursday of the existence of a program launched in 2007 called PRISM, which tracks information from nine leading U.S. Internet companies: Microsoft, Yahoo, Google, Facebook, AOL, YouTube, Apple, PalTalk and Skype.

In response to a question after his speech, Obama defended the programs as essential to combating terrorist threats. “They may identify potential leads with respect to folks who might engage in terrorism,” he said.

He also argued that some have overstated the impact of the programs. “Some of the hype we’ve been hearing over the past day or so - nobody has listened to the content of people’s phone calls,” he said.

Agencies add: US spy chief James Clapper also strongly defended government surveillance programmes after revelations of phone records being collected and internet servers being tapped.

He said disclosure of a secret court document on phone record collection threatened “irreversible harm”.

Revelations of an alleged programme to tap into servers of nine internet firms were “reprehensible”, he said.

The director of US national intelligence said he wanted to reassure Americans that the intelligence community was committed to respecting their civil liberties and privacy.

Meanwhile, the European Union said 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,” 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.