Donald Trump’s campaign advisers, including ousted national security adviser Michael Flynn, had contacted Russian officials or others with ties to the Kremlin at least 18 times in the final months of the 2016 presidential election, Reuters reported on Thursday.

Six of the previously undisclosed contacts — which included phone calls and emails — were between Russian Ambassador Sergey Kislyak and Flynn, whom Trump fired in February for concealing his meetings with the Moscow envoy from the White House and Vice President Mike Pence, the report said, citing three current and former US officials.

Flynn and Kislyak stepped up their conversations after the Nov. 8 election when the two talked about creating a back channel for communication between Trump and Russian President Vladimir Putin that would bypass the national security community, the report said.

Other discussions from April 2016 to November 2016 between Russian officials and campaign operatives involved improving economic relations between the two countries and fighting the Islamic State.

The US officials told the news wire service that they did not see any evidence of wrongdoing or collusion between the campaign and Russian officials in the communications that had been reviewed so far.

The revelations in the report came a day after the Department of Justice appointed former FBI Director Robert Mueller as a special counsel to investigate what role Russia played in the election and whether Trump campaign officials colluded with Moscow.

Two congressional panels are also probing the same claims.

The White House did not respond to requests for comment. Flynn’s lawyer declined to comment. A Russian Foreign Ministry official in Moscow declined to comment on the contacts and referred Reuters to the Trump administration.