(CNN) Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee, rejected Republican Chairman Richard Burr's recent statements that the committee has not found evidence of collusion, saying the investigation is still ongoing and the committee still had to interview key witnesses.

"Respectfully, I disagree," Warner said Tuesday. "I'm not going to get into any conclusions I've reached because my basis of this has been that I'm not going to reach any conclusion until we finish the investigation. And we still have a number of the key witnesses to come back."

Warner's comments represented a rare public split for the leaders of the Senate Intelligence Committee, which has been the only congressional panel that has kept its investigation into Russia's 2016 election meddling on a bipartisan track.

Burr and Warner have managed to conduct a bipartisan investigation for more than two years, as their staffs have quietly interviewed more than 200 witnesses and reviewed more than 300,000 pages of documents as part of the probe. But they have put off making conclusions about the collusion question, and the split is a signal that they could struggle to stay on the same page as the committee attempts to write its report on 2016 election meddling.

Last week, Burr told CBS News that the committee did not have facts indicating collusion between the Trump campaign and Russia.

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