John Lewis, one of America's most revered civil rights leaders, says Snowden, who has come in for some harsh criticism from the Obama administration for leaking details of classified surveillance programmes, was continuing the tradition of civil disobedience.

"In keeping with philosophy and discipline of non-violence, in keeping with teaching of Henry David Thoreau and people like Gandhi and others, if you believe something that is not right, something is unjust, and you are willing to defy customs, traditions, bad laws, then you have a conscience. You have a right to defy those laws and be willing to pay the price," Lewis told Guardian.

Lewis, the man whom Obama called the "conscience of the US Congress", said Snowden could claim he was appealing to "a higher law" when he disclosed top secret documents of NSA.