Washington: A defiant Herman Cain declared he would not end his bid for the Republican presidential nomination in the face of allegations of sexual harassment and called his latest accuser a tool of the "Democrat machine" in America.

Cain spoke at a news conference in Arizona on Wednesday, one day after Sharon Bialek became the fourth woman to lodge complaints of unwanted sexual advances and the first to go public.

He denied that he even knew Bialek, who accused Cain of making an unwanted sexual advance while she was asking for help finding a job.

Asked about the motivations of the women coming forward long after the alleged incidents, Cain told the news conference, "The machine to keep a businessman out of the White House is going to be relentless."

"We will get through this," he added, trying to steady a campaign that has made him the leader in an unofficial race to emerge as the principal conservative rival to former Massachusetts Governor Mitt Romney.

A political novice, Cain shot to the top of opinion polls with small government, anti-tax tea party activists and other conservatives flocking to the former pizza chain CEO with his tell-it-like-it-is style and outsider image.

But, since October 30, Cain has been dogged by accusations from women that he acted inappropriately towards them while he headed the National Restaurant Association in the 1990s.