Washington (CNN) Former Trump campaign adviser Roger Stone denied a report Tuesday that he told associates he was in contact with WikiLeaks founder Julian Assange in 2016.

An unnamed source told The Washington Post that Stone had a phone conversation with Assange in the spring of 2016. Ahead of any public knowledge about Democratic email leaks, Stone told the source he had learned WikiLeaks had obtained emails from the Democratic National Committee and Democratic presidential nominee Hillary Clinton's campaign chairman, John Podesta.

During the campaign, Stone said in interviews and speeches that he was in touch with WikiLeaks, and he posted tweets in October 2016 that seemingly predicted the Podesta leaks. The Washington Post report suggests that in addition to these public statements, Stone was even more candid in private conversations about ties to WikiLeaks.

Sam Nunberg, the Trump associate who went on a national media spree last week saying he would not comply with special counsel Robert Mueller's demand to hand over his emails pertaining to the campaign ( he later backed down ), also told the Post that Stone had contact with Assange in 2016.

On CNN's "Anderson Cooper 360" Monday night, Nunberg said that Stone -- who he has called a mentor -- was "a subject" in the special counsel's investigation.

"I think it's pretty obvious that they're asking me about Roger Stone and Julian Assange," Nunberg said, later adding, "At the very least, he is a subject."

Stone, who briefly served as a Trump campaign adviser early in the race, strongly denied contact with Assange despite earlier public claims that he's spoken with him. He was dismissive of Nunberg's most recent claims, saying in a statement to CNN on Tuesday that his protege misinterpreted a joke.

"Late one Friday night, when I was trying to get Sam off the phone, Sam asked if I had plans for the weekend and I said I was 'flying to London to have dinner with Julian Assange' -- a joke -- and hung up," Stone said, later adding that Nunberg "was too intense to figure out it was a joke."

"My passport shows I never left the country in 2015 or 2016 and surveillance cameras for a guy in a virtual gulag at the Ecuadorian Embassy show he never left there and I never arrived there," Stone continued, referring to Assange.

Stone also denied knowing about any leaks beforehand or receiving "any allegedly hacked material from any source and pass them on to Donald Trump or the Trump campaign."

WikiLeaks has said it has never been in contact with Stone. The Atlantic reported in February, however, that Stone and WikiLeaks did exchange private, direct messages on Twitter.

In November, CNN reported that Stone was in contact with New York radio personality Randy Credico, who Stone referred to as the intermediary between him and Assange, according to sources familiar with the situation. Stone insisted there was nothing untoward about their conversation. Credico has interviewed Assange and visited him in person.

Stone said in his Tuesday statement that "Credico's confirmation that WikiLeaks would publish non-specific Clinton material predates his meeting and first interview with Assange is irrelevant."

Stone also tweeted ominous messages ahead of leaks, including one that said "Payload coming. #Lockthemup" two days before WikiLeaks published a trove of Podesta's emails.