Michael Flynn and other Donald Trump campaign advisers contacted or were in contact with Russian officials at least 18 times via phone and email in the last seven months of the 2016 presidential race, Reuters reported.
Six of those undisclosed contacts were phone calls between Trump advisers, such as former national security adviser Michael Flynn, and Russian ambassador Sergei Kislyak.
Conversations between Flynn and Kislyak reportedly involved establishing a back channel for Trump and Russian President Vladimir Putin to communicate, bypassing the U.S. national security bureaucracy.
Early this year, the Trump White House denied any contact with Russian officials during the 2016 presidential election.
The sources who described the contacts to Reuters said they saw no evidence of wrongdoing in the undisclosed communications that have been disclosed so far, but such a revelation could increase pressure on Trump and his aides to give the FBI and Congress the full story in terms of interactions with Russian officials.
Members on the Senate and House intelligence committees have reviewed transcripts and documents at the CIA related to contact between Trump campaign advisers and Russians officials.