Google has sharply challenged the US government’s gag order on its internet surveillance programme, citing what it described as a constitutional free speech right to divulge how many requests it receives from the government for data about its customers in the name of national security.

The US government is considering whether to charge Edward Snowden with leaking classified surveillance secrets, while it defends the spy programme it says keeps America safe from terrorists.

The US government has admitted that a top spy agency was using a “crucial tool” against terrorism by sweeping up domestic telephone records, but new revelations on the practice sparked a swift backlash.

The White House has defended the government’s need to collect telephone records of American citizens, calling such information “a critical tool in protecting the nation from terrorist threats”.