U.S. President Donald Trump discounted allegations of sexual assault against Roy Moore and said Tuesday that voters should not support the Alabama Republican Senate nominee's "liberal" rival.

Trump addressed the swirling controversy surrounding Moore for the first time since top Republican leaders called on Moore to step aside more than a week ago.

"We don't need a liberal person in there," Trump said of Moore's rival, Democrat Doug Jones. "We don't need somebody who's soft on crime like Jones."

Trump said he will announce next week whether he will campaign on Moore's behalf. Trump spoke to reporters Tuesday at the White House before leaving for a Thanksgiving break at his Mar-a-Lago estate in Palm Beach, Fla.

Six women have accused Moore of pursuing romantic relationships with them when they were teenagers and he was an assistant district attorney in his 30s. Two have accused him of assault or molestation. Moore has denied the allegations.

Trump dismissed questions from reporters about him backing a man accused of sexual assault over a man who is a Democrat. He pointed to Moore's assertion that the candidate did nothing wrong.

"Roy Moore denies it, that's all I can say," Trump said.

"He totally denies it."

He also noted that the allegations came from behaviour alleged to have happened decades ago.

"Forty years is a long time," Trump said, questioning why it took so long for Moore's accusers to come forward.

Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan, both Republicans, have called on Moore to leave the race in light of the accusations. The Republican National Committee and the National Republican Senatorial Committee have pulled their support for Moore's campaign.

The special election for the Alabama Senate seat is Dec. 12.

Previously, White House press secretary Sarah Huckabee Sanders had said only that Trump "thinks that the people of Alabama should make the decision on who their next senator should be.

Moore's campaign has taken aim at the credibility of accuser Beverly Young Nelson, who claims Moore sexually harassed her when she was 16. (Lucas Jackson/Reuters)

"The president said in his statement earlier this week that if the allegations are true then Roy Moore should step aside. He still firmly believes that," Sanders said last week.

The allegations against Moore come amid a national reckoning over misdeeds by powerful men in media, business and politics. Trump said he is "very happy" that women are speaking out about their experiences.

"I think it's a very special time because a lot of things are coming out and I think that's good for our society and I think it's very, very good for women," Trump said.

More than a dozen women came forward in the waning days of the 2016 presidential election to say that Trump had sexually assaulted or harassed them over the years. He denied it. He was also caught on tape in 2005 boasting that he could grab women's private parts. "When you're a star, they let you do it," Trump said on the Access Hollywood tape.

Trump declined to answer Tuesday when asked why he does not believe Moore's accusers.

Republican statements used in anti-Moore ad

Jones began airing a new ad Monday that features statements made by Attorney General Jeff Sessions, U.S. Sen. Richard Shelby of Alabama and first daughter Ivanka Trump responding to allegations of sexual misconduct against Moore.

Sessions said he had no reason to doubt Moore's accusers. Shelby, a Republican, said he will "absolutely not" vote for Moore. Ivanka Trump said there's a special place in hell for people who prey on children.

The ad was the first direct assault by the Jones camp against Moore regarding the allegations.

Moore's camp has begun firing back at the media and one of the accusers. His campaign held a Tuesday afternoon news conference to publicly question the account of Beverly Nelson, who said Moore assaulted her when she was a 16-year-old waitress.

The campaign quoted two former restaurant employees and a former customer who said they did not remember Nelson working there or Moore eating there.