An influential Senate Democrat warned on Friday that attempts to expose an FBI source during an active investigation was "potentially illegal," amid reports that a secret informant has fed the bureau information relevant to the ongoing probe of Russia's electoral interference.

With questions still being raised about what Trump campaign officials knew about Russian meddling in the 2016 election, news reports this week suggested that a confidential source has provided the FBI with intelligence on the matter.

Earlier this week, President Donald Trump reacted to the suggestion of potential FBI spying as being "bigger than Watergate." Meanwhile, The Washington Post reported this week that allies close to the president were working to expose the source.

However, Virginia Senator Mark Warner, the top Democrat on the Senate Intelligence Committee, said in a series of posts on Twitter Friday that attempting to unmask a confidential source was "irresponsible" and "potentially illegal"— potentially opening up a new front between Trump and those he views as political antagonists.

"Publicly outing a source risks not only their life, but the lives of every American, because when sources are burned it makes it that much harder for every part of the intelligence community to gather intelligence on those who wish to do us harm," Warner posted on Twitter, as he linked to The Post's article.

WARNER TWEET

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

Trump and the FBI have been locked in an unprecedented public battle. The president and his allies have long complained about a "deep state" agenda of government officials actively working to undermine his presidency.

In an interview with The Post this week, former New York City Mayor Rudolph Giuliani — Trump's personal lawyer — accused law enforcement officials of "covering" for actions committed by the Obama administration.

Giuliani added that an informant could make Special Counsel Robert Mueller's investigation "completely illegitimate."