© Reuters/Jonathan Ernst/File PhotoAlabama Republican candidate for U.S. Senate Roy Moore speaks with reporters as he visits the U.S. Capitol in Washington, U.S. October 31, 2017.
Moore, 70, the state's former chief judge, vehemently denied the allegations, calling them "completely false and a desperate political attack."
U.S. President Donald Trump would want Moore to step aside if the allegations against him are true, White House press secretary Sarah Sanders said on Friday.
"Like most Americans, the president believes we cannot allow a mere allegation, in this case one from many years ago, to destroy a person's life," Sanders said.
"However, the president also believes that if these allegations are true, Judge Moore will do the right thing and step aside," she said, as Trump arrived in Vietnam on his 12-day Asia tour.
In a series of Twitter posts later in the day, Moore cast the published allegations against him part of a bid to "silence and shut up Christian conservatives like you and me," adding "I will NEVER GIVE UP the fight!"
Senate Republican leader Mitch McConnell, working with a slim 52-48 majority, called on Moore to drop out of the race "if these allegations are true." Several other Republicans, including Texas Senators John Cornyn and Ted Cruz, and Utah Senator Mike Lee, all of whom endorsed Moore, echoed that sentiment.
At least two Republican senators, John McCain of Arizona and John Thune of South Dakota, said Moore should step aside immediately, with McCain calling the accusations "deeply disturbing and disqualifying."
Leigh Corfman, now 53, told the Post she met Moore at a courthouse in 1979 when Moore offered to keep her company on a bench outside of a hearing room while her mother was inside for child custody proceeding.
Moore, at the time an assistant district attorney, asked for the girl's phone number and days later took her to his house, where they engaged in sexual activity before she asked to be taken home, Corfman said.
The story also quoted three other women who said Moore dated them when they were between 16 and 18 years of age and he was in his early 30s, though none said they had sexual contact with Moore.
Reuters was unable to independently confirm the allegations.
The Moore campaign accused the Post of colluding with Democrats to tarnish his reputation with false accusations.
The Post said none of the women had donated to or worked for Moore's Democratic opponent, Doug Jones, or for his Republican primary rivals, and that Corfman said she had voted for Republicans in the past three presidential elections, including for Donald Trump in 2016.
Comment: Before anyone picks up their pitchforks, lets keep in mind the principle that a person is innocent until proven guilty. Lets also remember that the story came first from the notorious fake news outlet Washington Post. For all we know, and assuming that the woman who made the accusations is real and is telling the truth, Moore might not have even been aware at the time that she was underage, and there is no reason to think the sexual encounter was forced on her.
While in the interest of justice we welcome revelations about real sexual predators, the fact is that in politics it is way too easy to make accusations without any evidence to discredit an opponent and even destroy their career.