The office of special counsel Robert Mueller, which is investigating Russian interference into the 2016 US presidential election, has confirmed to DW that it recently referred a case involving a potential campaign to discredit Mueller to the FBI.

Special counsel spokesman Peter Carr confirmed this in an email to DW, stating: "When we learned last week of allegations that women were offered money to make false claims about the special counsel, we immediately referred the matter to the FBI for investigation."

The fact that the special counsel's office has made the case public is seen by many as a sign of how seriously it is taking the threat. Many Trump allies have sought to publicly discredit Mueller, and the president himself has repeatedly decried the investigation as a "witch hunt."

Read more: Opinion: Motives behind GOP-Nunes memo release deeply troubling

Woman claims she was contacted by GOP lobbyist

The woman's identity is currently unknown, but she recently contacted a number of journalists with allegations that she had been offered $20,000 (€17,632) to provide false testimony as a way to discredit Mueller. The special counsel's office says it was alerted to the matter by journalists following up on emails from the woman.

In her correspondence with journalists, the woman says she was contacted by a man claiming to work for Republican lobbyist and right-wing radio host Jack Burkman. Burkman, who peddles conspiracy theories on his radio program, has posted Facebook videos accusing Mueller of being an alcoholic and sexual abuser.

He also took to Twitter to make similar claims. So far, however, he has offered no proof to back them. Burkman's program is also carried by Newsmax TV, which is owned by Trump confidant Chris Ruddy.

Clear about what he wanted

The woman told The Atlantic magazine, which broke the story, that the man who contacted her was clear about what he wanted, telling her: "I want you to make accusations of sexual misconduct and workplace harassment against Robert Mueller, and I want you to sign a sworn affidavit to that effect."

She told the magazine that she had worked for Mueller 44 years ago and had experienced no such harassment. She said the man "offered to pay off all of my credit card debt, plus bring me a check for $20,000 if I would do it. He knew exactly how much credit card debt I had, right down to the dollar, which sort of freaked me out."

To date, the Mueller team has charged 32 people with crimes related to Russian involvement in the 2016 election and possible collusion by President Donald Trump's election campaign.