Paul Manafort, former campaign chairman to President Trump, was wiretapped by U.S. investigators before the election and continuing into 2017, CNN reported.
Some of the communications intercepted prompted investigators to wonder whether Manafort encouraged Russia to help with Trump's presidential campaign, the news organization reported, citing three sources familiar with the probe.
Two sources warned, however, that the information was not conclusive, according to CNN.
The federal investigation team looking into Russian involvement in the U.S. election led by Robert Mueller has been made aware of the communications, CNN reported.
A secret order authorized by the court that oversees the Foreign Intelligence Surveillance Act focused on work done by a cluster of Washington consulting firms form Ukraine's former ruling party, CNN reported, citing sources.
The surveillance stopped because of lack of evidence but the FBI restarted it again this year after the court obtained a warrant extending into this year, according to CNN.
The second warrant was part of an attempt to investigate ties between Trump associates and suspected Russian operatives, CNN reported, citing sources.
Last fall, FBI interest in the case and in Manafort increased after the discovery of communications between Manafort and suspected Russian operatives and between Russians themselves, according to CNN. It was not clear whether communications by Trump were included in the surveillance, CNN reported.
The White House did not respond to CNN for comment.
In August, the FBI searched Manafort's home as part of the investigation into Russia's involvement in last year's general election.
The pre-dawn raid on July 26 focused on documents and other materials at Manafort's home in Virginia.