Emails purporting to show former Attorney General Loretta Lynch assuring Democratic operatives that the FBI would limit its investigation into the 2016 presidential nominee Hillary Clinton are not authentic, a spokesman for Ms. Lynch told Congress late Thursday.

“Those communications did not take place,” Robert Raben said in a letter to the Senate Judiciary Committee, which had demanded answers from the former attorney general.

Judiciary Chairman Charles E. Grassley had asked Ms. Lynch to clear up the matter after The New York Times and Washington Post reported in May that federal investigators had obtained documents that detailed communications between the attorney general and Clinton staffer Amanda Renteria where Ms. Lynch assured that the FBI’s probe wouldn’t delve too deeply.

Mr. Raben said nothing of the sort ever happened.

“Ms. Lynch does not know Ms. Renteria, did not discuss the Clinton email investigation with Ms. Renteria, and did not communicate to Ms. Renteria, either in words or in substance, that ‘she would not let the FBI investigation into Clinton go too far,’” the spokesman said.

“Likewise, to the best of her knowledge and recollection, neither Ms. Lynch nor any representative of the Office of the Attorney General discussed the Clinton email investigation with Ms. Renteria, [former DNC chairwoman] Representative Wasserman Schultz or her staff, or any DNC official,” Mr. Raben said.

The spokesman said Ms. Lynch couldn’t publicly answer two other questions from Mr. Grassley asking whether she was ever briefed about the documents obtained by federal investigators. But Mr. Raben hinted she would talk in close session.

Questions about the authenticity of the documents in investigators’ hands arose from the start. The Post reported that the information about the documents came from a Russian intelligence document that detailed the claim, supposedly made in an email between Ms. Schultz and liberal activists.

Mr. Raben said Ms. Lynch is prepared to cooperate with the Senate’s investigation into Russian meddling in the election and the aftermath, which now includes President Trump’s decision to fire FBI Director James B. Comey.

Mr. Comey, in blockbuster testimony last month, said Ms. Lynch had demanded that he shade the way he spoke about the Clinton probe in public, in what appeared to be an effort to soften potential political damage.