Former National Security Agency (NSA) contractor Edward Snowden has said he has "no chance" of a fair trial in the U.S. and has no plans to return there, BBC News reports.

He said that the 100-year-old law under which he has been charged "forbids a public interest defense".

"There's no way I can come home and make my case to a jury," he said in an online Q&A.

The 30-year-old has temporary asylum in Russia after leaking details of U.S. electronic surveillance programs.

He said that his predicament over not having a fair trial was "especially frustrating".

"Returning to the U.S., I think, is the best resolution for the government, the public, and myself, but it's unfortunately not possible in the face of current whistleblower protection laws, which, through a failure in law, did not cover national security contractors like myself," he told the Free Snowden website.

"Maybe when Congress comes together to end the programs... They'll reform the Whistleblower Protection Act, and we'll see a mechanism for all Americans, no matter who they work for, to get a fair trial."

In December, Snowden delivered an "alternative" Christmas message to Britain's Channel 4 TV, in which he called for an end to mass surveillance.

Earlier on Thursday, according to the BBC, an independent U.S. privacy watchdog ruled that the bulk collection of phone call data by U.S. intelligence agencies is illegal and has had only "minimal" benefits in preventing terrorism.

The Privacy and Civil Liberties Oversight Board advised by a 3-2 majority that the program should end. The report from the PCLOB is the latest of several reviews of the NSA's mass surveillance program, the details of which caused widespread anger after they were leaked by Snowden.

In a separate development on Thursday, U.S. Attorney General Eric Holder told told MSNBC television that he was unlikely to consider clemency for Snowden.

Holder said that the U.S. authorities "would engage in conversation" about a resolution of the case if Snowden accepted responsibility for leaking government secrets.

But he said granting clemency "would be going too far".