The U.S.'s National Security Agency has been using the world's biggest internet companies to spy on foreigners.

Leaked documents suggested the NSA was tapping directly into the servers of firms like Google, Facebook and Apple.

The head of the agency confirmed it has been collecting information - but only about non-U.S. citizens.

On Thursday it was revealed the NSA has been monitoring the phone records of milions of Americans.

In an interview with Al Jazeera, Declan McCullagh, an analyst at the CNET technology website, said that it is still unclear whether the internet tapping operation has the tacit approval of the biggest technology firms.