Former Trump 2016 campaign adviser George Papadopoulos claimed Monday several nations, including U.S. allies, had a "vested interest" against the then-candidate's 2016 platform.

Papadopoulos praised Attorney General William Barr and federal prosecutor John Durham for engaging with Australian, British and Italian officials, in an interview with Martha MacCallum on "The Story."

"Bill Barr and John Durham are not on a wild goose chase," he claimed. "These countries were willfully complicit in what I believe was an international conspiracy to undermine the Donald Trump campaign, and to assure that if he was elected president that he would be handcuffed because they had a vested interest in assuring that his America First policies would not be the ones that would be implemented."

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Last year, Papadopoulos served 12 days in prison in connection with then-Special Counsel Robert Mueller's Russia investigation.

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He had pleaded guilty to making false statements to federal prosecutors and spent those nearly-two-weeks in a Wisconsin facility.

Speaking with MacCallum, Papadopoulos appeared to nod to the events during the campaign that led to the Mueller team focusing on him.

"I lived it," he said. "I spoke to these diplomats and I know what they wanted."

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He also reacted to former Italian Prime Minister Matteo Renzi reportedly threatening to sue him for $1 million.

Papadopoulos noted Renzi was in office during Trump's campaign and claimed the ex-politician went "on a rant about the president and then says he wants to sue me."

"I welcome discovery in any lawsuit."

Barr sparked criticism in multiple countries in recent days, as he seeks assistance in studying the Russia investigation's origins, according to the Wall Street Journal.

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A Justice Department official told Fox News on Monday that Attorney General Bill Barr asked President Trump to make introductions to foreign countries that might have had information pertinent to U.S. Attorney John Durham's ongoing probe into possible misconduct by the intelligence community at the outset of the Russia investigation.

But, a person familiar with the situation told Fox News it would be wrong to say Trump "pressed" the Australian prime minister for information that could have discredited Mueller's now-completed probe, as The New York Times reported earlier Monday.

Fox News' Brooke Singman contributed to this report.