Her allegations, in a video clip posted on the pro-Donald Trump website Breitbart.com, appear just hours before the Republican presidential candidate debates his Democratic opponent Hillary Clinton, Bill's wife.
Leslie Millwee, a former reporter for local Arkansas TV station KLMN-TV, said she interviewed Clinton some 20 times in public when he was governor of the southern US state.
Millwee - then known as Leslie Derrick - told Breitbart that Clinton visited the TV station and assaulted her in the editing room in all three cases.
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"I was sitting in a chair," she said about what she described as the first assault. "He came up behind me and started rubbing my shoulders and running his hands down toward my breasts. And I was just stunned. I froze. I asked him to stop. He laughed."
On another occasion, she said, Clinton rubbed his genitals against her as she protested.
After the third assault, Clinton visited her apartment, she added, saying she refused to let him in.
Millwee said she had thought of coming forward when the Monica Lewinsky White House sex scandal broke in 1998, but refrained to protect her young children.
"I think there's still no accountability in the media for the behavior of the Clintons, and if it affects the media and affects the election, so be it," she said.
"I'm sure I'm not the only woman who went through this kind of things with Bill Clinton."
However, the ex-reporter gave a different version of the story in a book published in 2011, mentioning only that Bill Clinton touched her shoulder, according to Breitbart.
The Clinton campaign dismissed her accusations.
"I wouldn't be surprised if Donald Trump seeks to invoke this report tonight or in the coming days," Hillary Clinton spokesman Brian Fallon said on MSNBC.
"We expect that he'll do anything in the closing days. He said he's practicing a scorched earth approach to the campaign."
The new revelations surfaced as Trump faces a string of accusations of sexual misconduct. The bombastic billionaire has blamed the Clinton campaign and the news media for the stories.
Trump recruited Breitbart.com CEO Stephen Bannon to be his campaign manager in August.
