California Sen. Dianne Feinstein says she sent a letter to the FBI regarding Supreme Court nominee Brett Kavanaugh.

The contents of the letter are not public.

WASHINGTON — Democratic Sen. Dianne Feinstein on Thursday said she referred a letter to the FBI about President Donald Trump's Supreme Court nominee Brett Kavanaugh, though the contents or subject of the letter are not yet public.

"I have received information from an individual concerning the nomination of Brett Kavanaugh to the Supreme Court," Feinstein said in a statement on Thursday. "That individual strongly requested confidentiality, decline to come forward or press the matter further, and I have honored that decision. I have, however, referred the matter to federal investigative authorities."

Feinstein's statement comes after a report in the Intercept on Wednesday noted that she had been withholding the document from other lawmakers, even fellow Democrats on the Judiciary Committee.

According to the Intercept, the letter originated with California Rep. Anna Eshoo, who may have received it from a constituent in the San Francisco Bay Area "affiliated" with Stanford University. The author of the letter is reportedly being represented by attorney Debra Katz, who works with victims of sexual abuse and harassment.

White House spokesperson Kerri Kupec responded to Feinstein's admission by calling it an attempt to delay Kavanaugh's confirmation.

"Throughout his confirmation process, Judge Kavanaugh has had 65 meetings with senators—including with Senator Feinstein—sat through over 30 hours of testimony, addressed over 2,000 questions in a public setting and additional questions in a confidential session," Kupec told the White House pool. "Not until the eve of his confirmation has Sen. Feinstein or anyone raised the specter of new ‘information’ about him."

"Throughout 25 years of public service, the Federal Bureau of Investigation has thoroughly and repeatedly vetted Judge Kavanaugh, dating back to 1993, for some of the most highly sensitive roles. He has served in the Office of Independent Counsel, the White House, and on the D.C. Circuit Court of Appeals, all before his nomination earlier this year to serve as Associate Justice on the Supreme Court," Kupec added. "Senator Schumer promised to ‘oppose Judge Kavanaugh’s nomination with everything I have,’ and it appears he is delivering with this 11th hour attempt to delay his confirmation."

The news comes after Kavanaugh's marathon confirmation hearings concluded late last week.