Donald Trump assailed as "absolutely false" the allegations by several women that he groped them, and blamed Democratic rival Hillary Clinton, the media and lobbyists of being engaged in a vicious effort to stop him from winning the White House.
With his numbers dropping in opinion polls only weeks before the 8 November election, the Republican presidential nominee told supporters at a rally in Florida that his campaign was engaged in "a struggle for the survival of our nation."
Mr Trump said accusations that he groped women in a series of incidents going back to the 1980s were part of a coordinated attempt to keep him from the Oval Office.
He said: "These vicious claims about me of inappropriate conduct with women are totally and absolutely false," adding that "the Clintons know it."
He said he would make public at some point evidence to dispute the charges.
Mr Trump spoke after The New York Times reported that two women said they had endured sexual aggression from him, and several other women made similar allegations in other media outlets.
Earlier, the newspaper said that it stands by its story and rejected claims by a lawyer for Mr Trump that the story is libelous.
"Nothing in our article has had the slightest effect on the reputation that Mr Trump, through his own words and actions, has already created for himself," David McCraw, vice president and assistant general counsel for the newspaper, said in a letter to Mr Trump's lawyer.
If Mr Trump disagrees that the story was libellous, "we welcome the opportunity to have a court set him straight," Mr McCraw said in the letter.
Meanwhile, the US First Lady Michelle Obama has criticised the Republican nominee in scathing terms in a campaign speech for Mrs Clinton in New Hampshire.
She described Mr Trump as "a powerful individual speaking freely and openly about sexually predatory behavior."
"It's one of countless examples of how he has treated women his whole life and I have to tell you that I listen to all this and I feel it so personally," she said.
The report in The New York Times was followed by a number of similar allegations from other women, putting more pressure on the Trump campaign as it lags in national opinion polls.
It is struggling to contain a crisis caused by the candidate's comments about groping women without their consent, which surfaced last Friday.
One of the women, Jessica Leeds, appeared on camera on the New York Times' website to recount how Mr Trump grabbed her breasts and tried to put his hand up her skirt on a flight to New York in or around 1980.
The second woman, Rachel Crooks, described how Mr Trump "kissed me directly on the mouth" in 2005 outside the elevator in Trump Tower in Manhattan, where she was a receptionist at a real estate firm.
Mr Trump's campaign denied there was any truth to the New York Times accounts.
The phony story in the failing @nytimes is a TOTAL FABRICATION. Written by same people as last discredited story on women. WATCH!
— Donald J. Trump (@realDonaldTrump) October 13, 2016
"This entire article is fiction, and for the New York Times to launch a completely false, coordinated character assassination against Mr Trump on a topic like this is dangerous," the Trump campaign's senior communications adviser Jason Miller said in a statement.
The report comes just two days after a Reuters/Ipsos opinion poll showed one in five Republicans thought Mr Trump's comments about groping women disqualified him from the presidency, and put him eight points behind Democratic candidate Hillary Clinton among likely voters.
Within hours, several other media outlets published similar reports. People magazine published a detailed first-person account from one of its reporters, Natasha Stoynoff.
Ms Stoynoff said Mr Trump pinned her against a wall at his Florida estate in 2005 and kissed her as she struggled to get away.
The article included a denial from a Trump spokeswoman who called the story a "politically motivated fictional pile-on".
Around the same time, the Palm Beach Post reported a claim by Mindy McGillivray, 36, a woman in South Florida, that Mr Trump had grabbed her buttocks 13 years ago while she was working at his Mar-a-Lago estate as a photographer's assistant.
"There is no truth to this whatsoever," Mr Trump's spokeswoman Hope Hicks told the Post.
The reports come on the heels of a 2005 video that surfaced on Friday that showed Mr Trump bragging about groping women, kissing them without permission, and trying to seduce a married woman.
"I just start kissing them. It's like a magnet. Just kiss. I don't even wait," Mr Trump is heard saying on the tape.
Mr Trump said during the second presidential debate on Sunday that he had not actually done the things he had boasted about, and apologised for his remarks, which he called private "locker room talk."
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Clinton aides sought to minimise fallout over Keystone - emails
Meanwhile, Mrs Clinton's presidential campaign looked for ways to avoid damaging its relationship with the White House as she considered how to publicly announce her position on the controversial Keystone XL pipeline, according to emails published this week by WikiLeaks.
Her aides weighed having the Democratic candidate say she opposed the pipeline in a closed-door union meeting, leaking it to news media outlets or including it without fanfare in a policy fact sheet, the emails show.
Mrs Clinton eventually announced that she opposed the pipeline on 22 September 2015, at a town hall event in Des Moines, Iowa, early in the contest to win the Democratic presidential nomination.
President Barack Obama announced that he too opposed the project on 6 November 2015.
The WikiLeaks group released its latest batch of apparently hacked personal emails of Clinton campaign chair John Podesta yesterday.
Whether Mrs Clinton would oppose TransCanada Corp's pipeline to bring Canadian crude tar sands oil to refineries on the Gulf of Mexico was a major issue in her Democratic primary race against chief rival US Senator Bernie Sanders, who opposed the project.
Mrs Clinton was walking a fine line on supporting or opposing the pipeline.
The Keystone XL controversy put at odds labour unions, which thought the project would spur job creation, and environmentalists, who advocated moving away from tar sands-derived oil to cleaner forms of energy.
Mrs Clinton's decision was further complicated by the fact that the pipeline approval process began when she was Mr Obama's secretary of state from 2009-2013.
She said repeatedly that she would wait to announce her position until after the State Department had repeated its review of the project, in deference to her former boss. Privately, aides were figuring out the best way to announce her opposition to the project.
The Clinton campaign has declined to verify the authenticity of the Podesta emails released by WikiLeaks.
Mr Podesta told reporters on Tuesday that the Federal Bureau of Investigation had notified him it was investigating the "criminal" hack of his emails as part of a broader probe.
The White House last week formally accused Russia of hacking Democratic Party organisations in an effort to influence the presidential election, a charge Russia has denied.
