A new accuser has claimed she was sexually assaulted by Roy Moore in a locked car when she was a teenager in the 1970s, further rocking the Alabama Republican’s race for an open Senate seat.

The allegation came on the day Senate majority leader Mitch McConnell said Mr Moore should quit the contest, while Mr Moore fired back that it is Mr McConnell who should step down.

Even before the news conference by Beverly Young Nelson, Mr Moore’s campaign released a statement saying that lawyer Gloria Allred — representing Ms Nelson — “is a sensationalist leading a witch hunt”. It said Mr Moore is innocent and “has never had any sexual misconduct with anyone”.

US Senate candidate Roy Moore
Roy Moore’s campaign team have denied the claims (Brynn Anderson/AP)

In tears, Ms Nelson said in New York that when she was 16, Mr Moore offered her a ride home from the restaurant where she worked.

She accused him of touching her breasts and locking the door to keep her inside his car. She said he squeezed her neck while trying to push her head towards his crotch and tried to pull her shirt off.

He finally stopped and as she fell or was pushed out of the car, he warned her no one would believe her because he was a county district attorney, Ms Nelson said.

Beverly Young Nelson with her high school yearbook signed by Roy Moore
Beverly Young Nelson with her high school yearbook signed by Roy Moore (Richard Drew/AP)

Mr Moore was already battling allegations reported last week by the Washington Post that he had sexual contact with a 14-year-old girl decades ago when he was in his 30s and pursued romantic relationships with three other teenagers.

“I believe the women,” Mr McConnell said on Monday in response to a question at an appearance in Louisville, Kentucky. He said flatly that Mr Moore should step aside for another Republican candidate.

When the Post’s story first broke last Thursday, Mr McConnell said Mr Moore should step aside if the allegations were true.

The crossfire escalated a Republican civil war over Mr Moore’s Senate candidacy in a December 12 special election, which until last week’s allegations was viewed as an inevitable Republican win.