U.S. government officials intercepted conversations between Paul Manafort, President Trump's former campaign manager, and Russian individuals about the campaign.

It was revealed Monday that Manafort, who has been entangled in an FBI investigation, had been wiretapped by the U.S. government during and after the 2016 campaign.

The recordings retrieved from the wiretapping have been handed over to special counsel Robert Mueller, who is heading up the federal investigation into Russia interference in the 2016 election and possible collusion between the Trump campaign and the Kremlin, according to CBS News.

Paul Manafort's spokesman condemned recent reports that his client had been surveilled by federal officials. "If true, it is a felony to reveal the existence of a FISA warrant, regardless of the fact that no charges ever emerged," Jason Maloni said in an emailed statement on Tuesday.

Manafort has been a key figure in the investigation and Mueller's team is going back more than a decade investigating Manafort and his actions.