On Friday, Donald Trump urged voters to check out the supposed "sex tape" of a former Miss Universe backing his rival Hillary Clinton, provoking the Democrat to label him "unhinged" in a surreal new turn to the White House race.

In a pre-dawn Twitter rant, the Republican nominee accused Clinton of helping Alicia Machado to obtain citizenship in order to exploit her story against him.

The Venezuela-born Machado, who claimed that the billionaire bullied her mercilessly after she won the Trump-owned beauty pageant in 1996, has sought to public attention since Clinton raised her case at this week's presidential debate.

Trump, wrote, in one of a series of virulent tweets "Did Crooked Hillary help disgusting (check out sex tape and past) Alicia M become a US citizen so she could use her in the debate?"

Clinton has lashed out at Trump's history of abusive remarks that included humiliating Machado over her weight gain and Latina origins, nicknaming her "Miss Piggy" and "Miss Housekeeping."

The Democrat said that Trump's overnight attacks on the former beauty queen as new evidence that he has been lacking the steadiness to be president.

Clinton said in her own series of pointed tweets in response to his sex tape allegation , "This is... unhinged, even for Trump".

By Prakriti Neogi