Story highlights Mook says Russia was behind fake news on Facebook

He says Bannon is also behind fake news because of his role at Breitbart

Washington (CNN) Robby Mook, Hillary Clinton's former campaign manager, said that the US needs to investigate Russia "intervening in the election."

He told CNN's Jake Tapper during a discussion Thursday at Harvard Kennedy School's Institute of Politics that Russia is behind a lot of fake news on Facebook.

"I think (fake news) was a huge problem," Mook said. "I think there's a lot of things that we need to examine coming out of this. You just named one of them. Congress has got to investigate what happened with Russia here. We cannot have foreign, and foreign aggressors I would argue, intervening in our elections."

The full interview with Mook and Kellyanne Conway, campaign manager for Donald Trump's successful presidential campaign, will air Sunday on CNN's "State of the Union."

Mook also blamed Breitbart News, which President-elect Trump's senior adviser Steve Bannon used to run, for "peddling stories" that are fake.

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