(CNN) Senate Intelligence Chairman Richard Burr isn't ready to conclude there's been no collusion between President Donald Trump's campaign and Russia.

Trump has been repeatedly citing the North Carolina Republican to make his case that no collusion occurred during the 2016 election, from Twitter to Fox News interviews to the Oval Office.

But Burr told CNN on Thursday that while the President is right that his committee has found no "hard evidence" of collusion, the investigation isn't over.

"The President's using a quote from three weeks ago, that you heard that I said we didn't have any hard evidence," Burr said. "That's fine. But we have a lot of investigation left."

Burr and Sen. Mark Warner, a Virginian who's the top Democrat on the Intelligence Committee, have been leading an investigation into Russia's involvement in the 2016 election that's largely remained bipartisan. While they have issued findings on matters like election security and the intelligence community's assessment, they still are working on the collusion element of the probe, which they've saved for last.

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