An Alabama woman on Monday accused Roy Moore, the state's Republican nominee for U.S. Senate, of sexual assault, alleging that he attacked her behind the restaurant where she worked when she was 16 and he was 30.

Beverly Young Nelson, who will be 56 on Tuesday, is the fifth woman to accuse Moore of making romantic or sexual advances toward them when they were teenagers, and the first to allege assault. The previous accusations were made in The Washington Post last week.

Joined by attorney Gloria Allred, Nelson said that Moore, then deputy district attorney of Etowah County, Alabama, began flirting with her when she was 15. He was a regular at the Gadsden restaurant where she worked, she said, and he would often pull her long red hair as she walked by.

"Mr. Moore was an adult, he was much older than I was," Nelson said. "I did nothing to encourage his flirtatious behavior. I was accustomed to men flirting with me."

She added that she did not respond to any of Moore's advances, because she had a boyfriend and was not interested in dating a much-older man.

But in December 1977, when she was 16, Nelson told reporters, Moore offered her a ride home after a late shift. But instead of driving her home, Nelson alleges that Moore parked his car in a dark spot behind the restaurant, locked her in and began groping her breasts. She said he attempted to force her head toward his crotch, causing bruising around her neck.

"I was terrified. He was also trying to pull my shirt off. I thought he was going to rape me. I was twisting, I was struggling, and I was begging him to stop," she said. "At some point, he gave up. He then looked at me and he told me, he said, 'You’re just a child,' and he said, 'I am the district attorney of Etowah County, and if you tell anyone about this, no one will ever believe you.'"

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A week before the alleged assault, she said he asked to sign her yearbook. Nelson read the inscription to reporters: "'To a sweeter, more beautiful girl, I could not say Merry Christmas. Christmas 1977. Love Roy Moore, Old Hickory House'...He signed it: Roy Moore, D.A.”

One of the women in The Washington Post report last week said that Moore had initiated unwanted sexual contact with her when she was 14 and he was 32. The Post also interviewed three other women who claim Moore had "pursued" them when they were 16 to 18 and he was in his early 30s.

Moore has called the accusations false and politically motivated. At an event in Alabama over the weekend, he said of the other accusers, "To think grown women would wait 40 years before a general election to bring charges is unbelievable."

Nelson said Monday that she had been too scared of Moore, who served as the deputy district attorney for Etowah County from 1977 to 1982 before going to be elected twice to the state's Supreme Court, to speak publicly sooner. She was inspired, she said, by the women who told their stories to the Post.

“My husband and I supported Donald Trump for president. This has nothing whatsoever to do with the Republicans and Democrats," Nelson said. "This has everything to do with Mr. Moore’s sexual assault.”

After the alleged assault, Nelson said, she quit her job at the restaurant. Nelson also said that prior to her decision to speak up at Monday's news conference, she had told just three people in her life: Her younger sister two years after the alleged assault occurred; her husband before they got married 13 years ago; and finally her mother, four years ago.

"In the days following, I covered the bruising on my neck with makeup. I did not tell anyone about what had happened — I was scared — I felt that if I told anyone what happened Mr. Moore would do something to me or my family," she added. "If I thought I was Mr. Moore's only victim, I probably would have taken what happened to me to the grave."

Allred, who noted that Nelson approached her rather than the other way around, challenged Moore to testify under oath in front of the Senate Judiciary Committee in a public hearing and said Nelson would voluntarily do the same.

NBC News has not independently confirmed the details of the alleged assault, and has reached out to Moore's campaign for comment.

Moore denied all claims of sexual misconduct in a statement released by the campaign ahead of the press conference.

“We’ve said this before and we’ll say it again: Judge Moore is an innocent man and has never had any sexual misconduct with anyone," Moore's campaign said.

In a news conference Monday evening, Moore called Nelson's allegation an "absolutely false" political maneuver, and said that he does not know her. He also said he did not know where the Gadsden restaurant is that Nelson alleged the assault took place.

Earlier in the day, top Senate Republicans strengthened their calls for Moore to step aside, with Senate Majority Leader Mitch McConnell adding that he believed the women.

Moore said he will not leave the race, firing back Monday that it is McConnell who "should step aside" because he's "failed" conservatives.

Sen. Cory Gardner of Colorado, chairman of the National Republican Senatorial Committee, said that if Moore wins the seat, the Senate should vote to expel him.

Sen. John Cornyn of Texas said in a statement that he no longer endorsed Moore, leaving just two Republican senators, Rand Paul of Kentucky and Ted Cruz of Texas, supporting him.