Though Hayden didn’t specify exactly what list he had in mind, the idea was crystal clear and fits with the threatening tone of previous statements he’s made on Snowden. He has previously equated Snowden’s hacktivist supporters to terrorists, dubbing them “twentysomethings who haven't talked to the opposite sex in five or six years” and labeled Snowden himself a ‘morally arrogant young man’ who will probably ‘end up like an alcoholic’.

Regardless, this latest 'kill list' remark is the most sinister of all Hayden’s thinly veiled threats towards Edward Snowden.

The NSA whistleblower has recently made the shortlist of finalists for this year’s Sakharov Prize for Freedom of Thought.

Snowden is wanted in the US on espionage charges, after leaking secret documents revealing the US surveillance program PRISM used to gather private data.

In August, he was granted temporary asylum in Russia, where he currently resides.

UPDATE: Mr. Hayden elaborated on his comments on Thursday via email to RT's Marina Portnaya.

"The quote is correct," writes Hayden. "I was intentionally broad and undefined and it was never a proposal."

"I never suggested he be put on any list. I simply reflected ruminations in my darker moments," he adds.