Washington (CNN) A woman is accusing Supreme Court nominee Brett Kavanaugh of assaulting her when they were in high school in the early 1980s, according to a source familiar with the allegations, which were relayed in a letter to Sen. Dianne Feinstein earlier this summer.

The letter details an incident when the woman, who has not come forward publicly, attended a party with Kavanaugh and others in a suburban Maryland home. Feinstein, the top Democrat on the Senate Judiciary Committee, has referred the letter to the FBI.

Kavanaugh physically pushed her into a bedroom, the accuser said. Along with another male, Kavanaugh locked the door from the inside and played loud music that the accuser said precluded successful attempts to yell for help.

Both men were drunk, she said, and Kavanaugh attempted to remove her clothes.

At one point, Kavanaugh was on top of her laughing as the other male in the room periodically jumped onto Kavanaugh.

Kavanaugh held his hand over her mouth at one point, and she said she felt her life was inadvertently in danger.

She said she was able to leave the room and go into a hallway bathroom. After Kavanaugh and the other male began talking to others in the house, she went home.

There is no indication the woman reported the incident to law enforcement at the time, but she said she has received medical treatment regarding the alleged assault. The woman also declined to come forward publicly after sending the letter to Feinstein. The accuser's name was redacted before Feinstein forwarded it to the FBI.

In a statement Friday, Kavanaugh denied the allegation.

"I categorically and unequivocally deny this allegation. I did not do this back in high school or at any time," he said.

Kavanaugh testified for three days before the Senate Judiciary Committee last week, where the issue was not raised. The Judiciary panel is scheduled to consider Kavanaugh's nomination next Thursday, and the full Senate may vote on confirmation later this month.

Judiciary Committee Chairman Chuck Grassley, R-Iowa, does not plan to postpone the vote.

"The Senate Judiciary Committee will vote on Judge Kavanaugh's nomination will proceed as scheduled, next Thursday," said Grassley spokesman George Hartmann.

The New Yorker first reported the details of the letter to Feinstein. The woman making the allegations declined a request from the magazine for comment.

Focus on Collins, Murkowski

In the first indication that they planned to mount a sustained defense of Kavanaugh, Judiciary Committee Republicans circulated a letter Friday signed by 65 women, vouching for Kavanaugh's character, who said they knew the nominee in high school.

But multiple GOP aides acknowledged that all eyes were focused on -- and waiting for -- the reaction of two senators: Susan Collins of Maine and Lisa Murkowski of Alaska.

Neither senator has said whether they would support Kavanaugh's nomination, and have continued to examine his record in the wake of the hearing.

Collins held an hour-long phone call with Kavanaugh on Friday -- a call that had been scheduled before the letter and allegations were made public. Her office declined to comment on details of the call.

Collins told reporters Thursday she didn't plan to say anything about the nomination until she had made a decision.

As to a strategy to shore up support from Murkowski and Collins, one senior GOP aide said it mainly came down to giving both senators their space, and being available to answer questions if they had them.

Timing of letter questioned

The timing of the letter has caused consternation on both sides of the aisle. Republicans charge that while it was dated on July 30, Feinstein only referred it to the FBI after the hearings had concluded with less than a week until the committee vote.

Some Democrats, meanwhile, were critical that Feinstein didn't share it earlier. But others say she was in a hard spot.

"Feinstein is in a tough position -- there are allegations made all the time against nominees and this one was particularly contentious," one Democratic aide said.

"The woman also reportedly asked for her name to be kept private, which, as a basic principle needs to be respected. And, finally, she would not have wanted this to be seen as simply a political attack. It's a difficult position for any member to be in," the aide added.

In a statement Thursday, Feinstein emphasized that the person asked not to be identified.

"That individual strongly requested confidentiality, declined to come forward or press the matter further, and I have honored that decision," Feinstein said.

The FBI confirmed it had received the referral from Feinstein.

"Upon receipt of the information on the night of September 12, we included it as part of Judge Kavanaugh's background file, as per the standard process," an FBI spokesperson said Thursday.

An FBI official says there is no criminal investigation into Kavanaugh as a result of this letter.

It is now part of Kavanaugh's background file and it will be up to the White House to determine whether there is any further action to take. The Judiciary Committee received an updated supplement to Kavanaugh's background investigation from the FBI Thursday afternoon, an aide said. Senators on the committee can now request access to that information.

Asked about actions as an adult

As part of her standard set of questions, Sen. Mazie Hirono, D-Hawaii, asked Kavanaugh at the hearing last week that if -- as an adult -- he'd ever made unwanted sexual advances. The line of questioning came before new allegations against Kavanaugh came to light.

Kavanaugh's age at the time of the alleged incident is unclear.

"As part of my responsibility, as a member of this committee, to ensure the fitness of nominees for a lifetime appointment to the federal bench, I ask each nominee two questions. First question for you, since you became a legal adult, have you ever made unwanted requests for sexual favors or committed any verbal or physical harassment or assault of a sexual nature?" Hirono asked.

Kavanaugh answered "no."

Since January 2018, Hirono has been asking the questions of all judicial nominees.

Hirono also asked if he'd faced any disciplinary action or "entered into a settlement related to this kind of conduct?"

Kavanaugh again said "no."