Joe Biden has denied allegations that he sexually assaulted a former aide in 1993.
In his first public remarks about Tara Reade’s claims, the former vice president said: “They aren’t true. This never happened.”
The presidential candidate added that he is asking the National Archives to determine whether there is any record of Ms Reade filing a complaint.
Ms Reade, who used to work in the Senate, has accused Mr Biden of pinning her against a wall, reaching under her skirt and assaulting her in the basement of an office.
Pressure on the 77-year-old mounted this week after Ms Reade’s brother and a former neighbour said she had previously told them about part of her allegation.
The Democrats’ likely candidate to take on Donald Trump in November’s election had not previously publicly spoken about the allegation, but his campaign put out a statement last month denying it.
On Friday, he added: “Women deserve to be treated with dignity and respect, and when they step forward they should be heard, not silenced.
“The second is that their stories should be subject to appropriate inquiry and scrutiny.”
He added that there are “inconsistencies in her story, which has changed repeatedly in both small and big ways”.
And he said Ms Reade says she raised “these issues” with his staff in 1993 but they have all denied this.
“News organisations that have talked with literally dozens of former staffers have not found one – not one – who corroborated her allegations in any way. Indeed, many of them spoke to the culture of an office that would not have tolerated harassment in any way – as indeed I would not have,” he added.
Mr Biden said there is a part of Ms Reade’s story that can be verified, and that is her claim she filed a complaint against him in 1993.
He said the only place the complaint could be is in the National Archives so he has requested for her complaint, if it is there, to be made available to the press.
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The Democrat added that he has spent his career “learning from women the ways in which we as individuals and as policymakers need to step up to make their hard jobs easier”.
He said he has fought for women’s health issues and basic women’s rights throughout his career and will continue to do so.
House of Representatives Speaker Nancy Pelosi said on Thursday that she still backed Mr Biden.
Mr Biden was also accused last year by another woman, Lucy Flores, of putting “a big slow kiss on the back of my head” during a campaign rally in 2014, but he said he was a tactile person and had never acted inappropriately.
Analysis: Each side will take what they want from this interview
By Amanda Walker, US correspondent
Finally, Joe Biden has responded to the allegation that has been public for weeks – that 27 years ago he sexually assaulted a former Senate employee, Tara Reade.
The gaffe-prone presumptive Democratic nominee agreed to speak about it publicly for the first time on what’s perceived as a friendly forum – MSNBC’s Morning Joe.
But presenter Mika Brzezinski did not go easy on him in what’s still unlikely to go down as a defining moment in this election campaign.
Brzezinski detailed the graphic claim that, in 1993, Mr Biden pinned her to a wall and touched her genitals.
Mr Biden’s answers were short and unequivocal – it did not happen, he said.
“This is an open book – there’s nothing for me to hide – nothing at all,” he told the programme.
Mr Biden’s silence over Tara Reade’s sexual assault allegation has frustrated both ends of the political spectrum.
Republicans have accused Democrats of double standards as the left has pitched itself as the side that believes women when they make allegations of sexual assault against powerful men.
Republicans still feel the sting of the confirmation hearings of Supreme Court Justice Brett Kavanaugh, in which Dr Christine Blasey Ford accused him of sexual assault.
Leading Democrats including Joe Biden said she should be given the benefit of the doubt as he now calls for due process in respect of his own allegation.
He was pushed repeatedly on this issue: “Are women to be believed unless it pertains to you?”
Mr Biden replied: “Look, women are to be believed given the benefit of the doubt, if they come forward and say something that they said happened to them, they should start off with the presumption they’re telling the truth. Then you have to look at the circumstances and the facts. And the facts in this case do not exist. They never happened. And there’s so many inconsistencies in what has been said in this case. So yes, look at the facts. And I assure you, it did not happen, period. Period.”
Arguably, Mr Biden did manage to maintain his Kavanaugh comments and his own position of denial by suggesting that an initial basis of belief can then be countered by lack of evidence, but that won’t stop accusations of hypocrisy.
Ms Reade says she made a formal complaint through the Senate Personnel Office. Mr Biden’s campaign says no such complaint was made and that he can prove that by asking the National Archive to release it if it exists.
His November opponent Donald Trump has been accused by numerous women of sexual assault and harassment. When asked about it on Thursday. he said he thought Biden should respond and that the allegation “could be false”, adding: “I know all about that.”
With a string of his own allegations, Mr Trump is not the right messenger to attack Mr Biden on this issue – he will likely leave that to his surrogates.
Each side will take what they want from this interview.
The allegation is getting more oxygen, which surely makes it harder for the impressive line-up of women who want to be Mr Biden’s running mate.
Most of them were adamant that Dr Blasey Ford should be believed – Republicans will be shouting from the rooftops that surely the same courtesy should be extend to Tara Reade.