Sen. Mark Warner Mark Robert WarnerIntelligence chief says Congress will get some in-person election security briefings Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' House approves bill to secure internet-connected federal devices against cyber threats MORE (D-Va.) warned Republican lawmakers on Friday not to expose the identity of a secret FBI informant, saying that to do so would be "irresponsible" — and potentially illegal.

"It would be at best irresponsible, and at worst potentially illegal, for members of Congress to use their positions to learn the identity of an FBI source for the purpose of undermining the ongoing investigation into Russian interference in our election," Warner, the top Democrat on the Senate Intelligence Committee, said in a statement.

"Anyone who is entrusted with our nation’s highest secrets should act with the gravity and seriousness of purpose that knowledge deserves," he added.

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Warner's comments come as some GOP lawmakers and allies of President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE seize on reports of an embedded FBI informant who fed investigators information about possible ties between the Trump campaign and Russia.

Some congressional Republicans have raised concerns that the FBI may have planted a mole within the Trump campaign in order to spy on the then-candidate and his team in the run-up to the 2016 presidential election.

Even Trump suggested on Thursday that the Obama administration had intentionally planted the informant in his presidential campaign, claiming that the matter could end up being "bigger than Watergate."

The New York Times reported last week that a top-secret FBI informant had met with two former Trump campaign advisers, George PapadopoulosGeorge Demetrios PapadopoulosTale of two FBI cases: Clinton got warned, Trump got investigated Trump says he would consider pardons for those implicated in Mueller investigation New FBI document confirms the Trump campaign was investigated without justification MORE and Carter Page.

The Washington Post reported on Thursday that allies of the president had begun waging a campaign to expose the role of the informant. In response, the FBI has been working to soften the blow if the source's identity is outed.