New York: CNN is suing the FBI for access to case files and other documents related to interviews with about 500 witnesses questioned during Special Counsel Robert Mueller's Russia probe.

The Federal Bureau of Investigation failed to respond to CNN's Freedom of Information Act request for the documents, known as "302s", the news organisation said in a suit filed in Washington on Tuesday. CNN is seeking a court order forcing the FBI to hand the documents over.

Special Counsel Robert Mueller breaks his silence on the Russia probe at the US Department of Justice last week. Credit:AP

"Despite numerous citations to 302s and other underlying documentation throughout the publicly-released version of the Special Counsel's Report - including many direct quotes from documents themselves - the FBI has failed to respond to CNN's request for the report's underlying evidence and factual findings within the time required by the FOIA."

Now that Mueller's two-year investigation into Russia's interference in the 2016 election is over, Democrats and news organisations have been battling for access to Mueller's underlying research and findings, including grand jury materials.