The writer E. Jean Carroll, who has accused Donald J. Trump of raping her in the 1990s and is suing him for defamation, asked on Thursday that he provide a DNA sample to determine whether his genetic material is on a dress she says she had on at the time of the incident.

The request for the DNA sample was made in a letter sent to President Trump’s lawyers via email, a spokeswoman for Roberta A. Kaplan, Ms. Carroll’s lawyer, said. Ms. Kaplan asked that the sample be turned over by March 2.

Lawrence S. Rosen, a lawyer representing the president in the defamation suit filed by Ms. Carroll, did not immediately respond to a request for comment.

The Associated Press was the first to report that Ms. Carroll was seeking the DNA sample.

The move comes amid a trial in the United States Senate that will determine whether Mr. Trump, who was impeached by the House, will be convicted and removed from office.