US spies on citizens and foreigners by tapping into web and phone traffic

US spies are secretly tapping into servers of nine internet giants including Apple, Facebook, Microsoft and Google in a vast anti- terror sweep targeting foreigners.

Stung by a dizzying 24 hours of revelations on covert programmes, the top US spy, James Clapper, slammed disclosure of information about the scheme, and warned that leaks about a separate programme to mine domestic phone records hurt US national security.

And yesterday US President Barack Obama defended his government's secret surveillance, saying Congress has repeatedly authorised the collection of records of Americans' phone use and foreigners' internet use.

Obama said safeguards were in place and that nobody was listening to the content of phone calls. And he said the internet targeting was aimed at foreign nationals, not American citizens.

The reports came as Obama was preparing to meet President Xi Jinping in southern California, a meeting intended to address among other things complaints about Chinese cyberattacks and spying. Now that conversation will take place amid discussion of America's own vast surveillance operations.

The Guardian and The Washington Post reported that the National Security Agency (NSA) had direct access to the servers of internet firms to track people's web presence via audio, video, photographs and e-mails.

Some of the biggest firms in Silicon Valley were caught up in the programme, known as PRISM, the reports said. They were Microsoft, Yahoo, Google, Facebook, Apple, PalTalk, AOL, Skype and YouTube.