(CNN) Hillary Clinton's campaign chairman John Podesta and former Democratic National Committee chairwoman Debbie Wasserman Schultz both privately denied to congressional Russia investigators that they had any knowledge about an arrangement to pay for opposition research on President Donald Trump, three sources familiar with the matter told CNN.

The interviews happened before this week's disclosure that the Clinton campaign and DNC paid for the research. Senate investigators may seek to further question the two top Democrats and dig deeper on the origins of the so-called Trump dossier, one of the sources briefed on the matter said.

Their remarks to congressional investigators raise the stakes in their assertion that they knew nothing about the funding because it's against the law to make false statements to Congress.

The White House has seized on the funding disclosures to discredit the ongoing investigations into potential collusion between the Russians and the Trump campaign. While the most salacious allegations in the dossier haven't been verified, its broad assertion that Russia waged a campaign to interfere in the election is now accepted as fact by the US intelligence community.

In recent closed-door interviews with the Senate intelligence committee, Podesta and Wasserman Schultz said they did not know who had funded Fusion GPS, the intelligence firm that hired British Intelligence Officer Christopher Steele to compile the dossier on Trump, the sources said.

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