Special counsel Robert Mueller said Tuesday that election meddling operations like those conducted by Russia during the 2016 presidential election are still occurring.

"Uncharged individuals and entities" are still engaging in operations similar to those charged in a case involving 13 Russian nationals and three entities accused of illegally interfering in U.S. politics, Mueller said.

He made the claim in a court filing that asked a judge to grant the special counsel's request to protect evidence in that case.

That protection plan would bar any of the defendants from reviewing the evidence found until they appear before a U.S. court. One of those defendants, Concord Management, has not agreed to that measure, according to the filing.