"The hundred-year old law under which I've been charged... forbids a public interest defence," he said in a question-and-answer session on the "Free Snowden" website on Thursday. (Agencies)
"This is especially frustrating, because it means there's no chance to have a fair trial, and no way I can come home and make my case to a jury," he said.
The comments during the former National Security Agency contractor's first such public forum since June. Snowden was asked about the conditions under which he would return to United States, where he faces espionage charges for leaking numerous documents about NSA surveillance programs.
"Returning to US, 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 said.
"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."
His comments came hours after a US government privacy watchdog panel said the NSA's indiscriminate collection of bulk phone records is illegal and has had minimal value in fighting terrorism.
Also on Thursday, US Attorney General Eric Holder said he was unlikely to consider clemency for Snowden. Holder told MSNBC television US 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."
"The hundred-year old law under which I've been charged... forbids a public interest defence," he said in a question-and-answer session on the "Free Snowden" website on Thursday.