Mueller's office interviewed Bannon last week regarding claims made privately by former Trump adviser Roger Stone about the emails from the DNC, which US prosecutors say were hacked by Russian operatives, the Washington Post reported on Tuesday citing people familiar with the investigation.
Mueller's office is trying to determine if WikiLeaks coordinated with Stone and the Trump campaign on the timing of the release of the emails, the report said.
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The special counsel is investigating allegations that Russia meddled in the 2016 US election and charges of collusion between Moscow and the Trump campaign. Russia and Trump have repeatedly denied the allegations.