|Cain, left, is competing with Perry, right, to be the main conservative challenger to Romney in the race [Reuters]
Republican US presidential candidate Herman Cain has accused rival Rick Perry's campaign of being behind recent sexual harassment claims against him as the 2012 White House race erupts into acrimony.
As reports surfaced of a third woman claiming she was harassed by Cain when he was leading the National Restaurant Association in the 1990s, Cain’s chief of staff Mark Block issued a scathing indictment of rival conservative Perry's camp, which he said had spread false allegations.
"It's an outrage," Block told Fox News. "The Perry campaign needs to apologise to Herman Cain and his family and America for this despicable action."
Cain and Perry are fighting it out to be the main conservative challenger to former Massachusetts Governor Mitt Romney in the race for the Republican nomination to take on President Barack Obama next year.
Perry spokesman Ray Sullivan denied the charge that the Texas governor's team was behind the sexual harassment claims that surfaced over the weekend on the Politico news website.
"Mr Block's claims are patently false. No one at our campaign was involved in this story in any way," he said.
The Perry camp also suggested Romney's campaign might have been responsible for the claims, but Romney spokeswoman Andrea Saul said this was "not true".
Cain, the former chief executive officer of Godfather's Pizza, has emerged from a fringe candidate to frontrunner despite never having held public office.
But the accusations of sexual harassment threatened to derail his chances to win the Republican nomination.
The AP news agency reported a third former employee said she considered filing a workplace complaint over what she saw as aggressive and unwanted behaviour by Cain when she worked for him.
The behaviour included a private invitation to his corporate apartment, she said.
One woman who accused Cain of sexual harassment had been given $35,000, a year's salary, in severance pay in the late 1990s, according to media reports.
'Trying to destroy me'
The controversy is a setback for Cain, whom a Quinnipiac University poll declared the leader in the Republican race with 30 per cent, followed by Romney with 23 per cent.
The poll was taken mostly before the allegations surfaced.
"There are factions that are trying to destroy me, personally, as well as this campaign," Cain said, speaking to technology executives in a Virginia suburb of Washington on Wednesday.
Chris Wilson, an Oklahoma political consultant with links to the Perry campaign, told local radio station KTOK he was a witness to one incident.
"I was the pollster at the National Restaurant Association when Herman Cain was head of it and I was around a couple of times when this happened and anyone who was involved with the NRA at the time, knew that this was gonna come up," he said.
Wilson said for legal reasons he could not discuss details of the incident, "but if she comes out and talks about it, like I said, it'll probably be the end of his campaign".
Cain said he expected his campaign would survive the controversy because of his popular support.
"There's a force at work here that is much greater than those that would try to destroy me, and destroy this campaign, and this journey to the White House. And that force is called the voice of the people," he said.