The wiretapping started before last November’s presidential election and continued into 2017, according to a report.
Some of the intelligence collected allegedly included communications that left investigators concerned that Mr Manafort may have encouraged Moscow to try and help the Trump campaign, claimed CNN.
In a separate report, the New York Times claimed that prosecutors working for Special Counsel Robert Mueller have told Mr Manafort - once one of Mr Trump’s closest advisors - that they are planning to indict him following a raid on his Virginia home in July.
Sources insist that the information gleaned from the bugs was inconclusive and the reports have not been confirmed by either the White House or Mr Manafort.
But the startling claim of government snooping could vindicate allegations made by the president in March that Mr Obama had his “wires tapped” at Trump Tower before his election triumph.
“Terrible! Just found out that Obama had my ‘wires tapped’ in Trump Tower just before the victory. Nothing found. This is McCarthyism!” the president had tweeted.
He added later: “How low has President Obama gone to tap my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!”
The claim was denied by the US Department of Justice but speculation was growing today that the FBI could have been listening in on conversations between Mr Trump and Mr Manafort.
CNN claims that Mr Manafort has been the “subject” of a probe dating back to 2014 connected to his work with the Ukrainian government.
A secret court order sought under the Foreign Intelligence Surveillance Act focused on work carried out by a group of Washington consulting firms for Ukraine’s former ruling party,
The initial wiretapping was stopped in 2016 through lack of evidence but it was restarted by the FBI earlier this year, said the cable network.
Insiders claim the second warrant was part of the probe into alleged links between Russian operatives and senior Trump campaign officials. In order to grant permission for the wiretapping, investigators needed to provide evidence of a suspicion that the target may be acting as “an agent of a foreign power”.
Mr Manafort has denied ever “knowingly” communicating with Russian spies during the election and is adamant he had no involvement in any attempts by the Kremlin to “undermine the interests of the United States”.
Mr Manafort was chairman of the Trump campaign from May to August last year. He stepped down following reports that he accepted payments linked to his work in Ukraine.
He was named as one of the trusted Trump aides who attended a meeting along with the president’s son, Donald Jr, and his son-in-law Jared Kushner with a Russian lawyer who claimed to have damaging information about Hillary Clinton’s campaign.