It has been revealed that US intelligence gathers around five billion telephone records a day for mobile phones around the world.
The National Security Agency can then track where individuals are, as well as retrace their movements and map out their relationships with other people.
The Washington Post exposed the extent of the surveillance using documents from former NSA contractor Edward Snowden.
US officials said the collection of data was lawful and only intended to develop intelligence about foreign targets.
But human rights organisation Amnesty International called it “the latest startling blow to the right to privacy” and said the US Congress must legislate to protect citizens.