Another woman accuses US senate candidate Roy Moore of sexual assault

A fourth woman has accused Alabama senate candidate Roy Moore of sexual assault as Republicans have increased calls for him to "step aside".

Beverly Young Nelson said she was 16 years old when Moore allegedly tried to force himself on her after offering a ride home from her job as a waitress, BBC reported on Monday.

"I tried fight him off while yelling at him to stop," she said, adding that he locked his car to prevent her escape.

Moore, 70, denies the allegations, describing them as a "witch hunt".

However, US Senate Republican leader Mitch McConnell said earlier on Monday that he believed the women accusing Moore of inappropriate behaviour.

Nelson's accusation comes after three other women detailed allegations of sexual assault by the conservative firebrand while they were teenagers in Alabama.

The 56-year-old said she met Moore at the Olde Hickory House restaurant in Gadsen, Alabama, where she worked as a waitress while she was a teenager.

She claimed Moore, a 30-year-old District Attorney at the time, offered to sign her high school yearbook and wrote: "To a sweeter more beautiful girl I could not say Merry Christmas. Christmas 1977. Love, Roy Moore, DA 12-22-77 Olde Hickory House."

At least a week later, he allegedly offered to drive her home and instead drove to the back of the restaurant car park.

"I was terrified. He was also trying to pull my shirt off. I thought he was going to rape me," she told reporters at a news conference on Monday.

"At some point he gave up and he then looked at me and he told me, '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", Nelson said, adding that her neck was bruised in the struggle.

"He finally allowed me to open the door and I either fell out or he pushed me out."

She added: "The passenger door was still open as he burned rubber, pulling away, leaving me laying there on this cold concrete in the dark."

Moore's wife also vehemently denies the allegations, contending that her husband's accusers are being paid.

McConnell told reporters in his home state of Kentucky on Monday that party officials were considering whether another Republican could challenge Mr Moore in next month's election, through a so-called write-in challenge.

He said Luther Strange, whom Moore beat in the Republican primary earlier this year, was a possible option.

Senator Cory Gardner, the National Republican Senatorial Committee chairman, said of Moore on Monday: "If he refuses to withdraw and wins, the Senate should vote to expel him, because he does not meet the ethical and moral requirements of the US Senate."