Former National Security Agency contractor Edward Snowden got into a heated exchange with comedian and late night host John Oliver over the ramifications of his wide-ranging leaks about U.S. surveillance apparatus during an interview that aired Sunday night.

“How many of those documents have you actually read?” Oliver asked Snowden, during an interview on his show, "Last Week Tonight."

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“I’ve evaluated all of the documents that are in the archive,” Snowden replied.

“You’ve read every single one?” Oliver asked.

“Well, I do understand what I’ve turned over," Snowden said.

"There’s a difference between understanding what’s in the documents and reading what’s in the documents,” Oliver replied, saying joking that “the last thing you’d want to do is read” thousands of complicated NSA documents.

Snowden noted that he was no longer in possession of the leaked files, and they had been passed along to journalists who were now analyzing them and deciding how to report on their contents.

Oliver was skeptical.

“So The New York Times took a slide, didn’t redact it properly, and in the end, it was possible for people to see that something was being used in Mosul on al Qaeda,” Oliver said.

“That is a problem,” Snowden replied.

“Well, that’s a f--- up,” said Oliver.

“It is a f--- up, and those things do happen in reporting,” Snowden said. "In journalism, we have to accept that some mistakes will be made. This is a fundamental concept of liberty."

“Right. But you have to own that then,” Oliver said, to a surprised Snowden. “You’re giving documents with information you know could be harmful, which could get out there.”

“You will never be completely free from risk if you if you’re free. The only time you can be free from risk are if you’re in prison,” Snowden said.

His appearance on the show comes as the surveillance programs he revealed receive new attention in Washington.

Last month, the Obama administration received court reauthorization of the NSA program collecting bulk data about phone calls.

The reauthorization comes before the June deadline for Congress to renew, replace or let expire the Patriot Act provision authorizing the surveillance program.