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(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.

“If we write a report based upon the facts that we have, then we don’t have anything that would suggest there was collusion by the Trump campaign and Russia,” Burr said.

A Democratic aide acknowledged that the committee has not uncovered direct evidence of collusion. But the aide argued that the number of episodes that have been discovered — among them the Trump Tower meeting with an offer for “dirt” on Hillary Clinton, former Trump campaign adviser George Papadopoulos being told by a London professor of “dirt,” Roger Stone’s connections to WikiLeaks and the Trump Tower Moscow discussions extending into the 2016 campaign — point to plenty of circumstantial evidence of collusion.

“None of those facts are in dispute,” the aide said. “Only what they mean.”

President Donald Trump has seized upon Burr’s statements to claim the committee has found no collusion, though Burr hedged his statement to CBS — and similar previous comments about finding evidence of collusion — by saying the investigation is not yet wrapped.

“The only thing I’ve addressed is whether we had facts that suggest there was (collusion). We don’t have any,” Burr told reporters on Tuesday. Asked whether the committee’s investigation exonerated Trump, Burr said: “Just saying what factually we’ve found to date. We haven’t finished our investigation.”

In the CBS interview, Burr suggested that the committee would focus on getting agreement on the facts, and let people make their own conclusions.

Warner noted that the committee is getting close to the end of its investigation, but there were still key witnesses to speak to, including Trump’s former lawyer Michael Cohen, whose scheduled Tuesday interview was postponed.

“What we do know, and it’s part of the public record, there’s never been a campaign in American history that during the campaign and its aftermath that the campaign folks affiliated with the campaign had as many ties with Russia as the Trump campaign did,” Warner said. “You get far down a thread and then it is interesting there are a number of the same people that ends up at the end of those threads, and many of those are the people we need to have come back and talk to us.”

Cohen was one of a number of witnesses, including Michael Flynn, Trump campaign chairman Paul Manafort and his deputy Rick Gates, that the committee wants to interview but has not yet since they were charged by the special counsel, the aide said, so the panel didn’t interfere with Mueller’s probe,

Warner told CNN last month the accidental disclosure from Manafort’s court filing that he was accused of sharing polling data with Konstantin Kilimnik — whom the special counsel has accused of having ties to Russian intelligence — was the “closest we’ve seen” to collusion.

CNN’s Michael Warren contributed to this report.