US mulling amnesty for Snowden?

US National Security Agency whistle blower Edward Snowden could be granted amnesty to return to the US if he agrees to stop leaking secret documents, a senior NSA official has hinted.

Richard Ledgett, the NSA official who is in charge of assessing the damage of the former NSA contractor's leaks, told CBS News that an amnesty, in his "personal view" is "worth having a conversation about".

"I would need assurances that the remainder of the data could be secured, and my bar for those assurances would be very high. It would be more than just an assertion on his part," he said in an interview with '60 Minutes' aired Sunday.

However NSA's director, Gen. Keith Alexander, told the same programme that, in his view, an amnesty would be a green light to potential whistleblowers.

"I think people have to be held accountable for their actions. Because what we don't want is the next person to do the same thing, race off to Hong Kong and to Moscow with another set of data, knowing they can strike the same deal," he said.

"This is analogous to a hostage taker taking 50 people hostage, shooting 10 and then say 'You give me full amnesty and I'll let the other 40 go'," Alexander added.

Snowden has revealed in previous interviews that the intelligence documents he leaked are no longer in his possession but in the hands of his trusted journalist partners Glenn Greenwald and Laura Poitras and that he did not take any intelligence material with him when he flew from Hong Kong to Russia.

Snowden, who has been granted asylum by Russia for 12 months, faces criminal charges in the US of theft of government property and "wilful communication of classified communications intelligence information to an unauthorised person".

Each of the charges carries a maximum 10-year prison sentence.

US intelligence officials assert Snowden stole more than 1.5 million classified documents detailing specific NSA programmes and operations, only a portion of which have been made public.

At the weekend, the NSA allowed a CBS television crew into their headquarters for the first time in its history, in an effort to be more open about what the agency does with the data it collects.