Papadopoulos told the Italian daily La Verita that he believed Renzi had acted on the orders of former U.S. president Barack Obama to "strike a low blow" against Trump in the run-up to the 2016 presidential election.

Renzi denied the allegation in a post on Facebook, saying Papadopoulos's accusation was "seriously damaging to my reputation." He added: "See you in court."

Former Italian prime minister Matteo Renzi said on Friday he would sue George Papadopoulos, a one-time campaign aide for U.S. President Donald Trump, over allegations that Renzi had tried to undermine Trump's 2016 election campaign.