Democratic US presidential nominee Hillary Clinton reacts as Republican US presidential nominee Donald Trump responds to a question about his remarks about women during their presidential town hall debate at Washington University in St. Louis, Missouri, US, October 9, 2016. [Photo/Agencies]

ST. LOUIS - A defiant Donald Trump on Sunday attacked former President Bill Clinton for his treatment of women and vowed, if he won the White House, to put Hillary Clinton in jail for operating a private email server while US secretary of state.

In a contentious town-hall debate, Trump, the Republican presidential candidate, said he would appoint a special prosecutor to look into his Democratic rival's email use because she had endangered national security during her tenure as President Barack Obama's chief diplomat from 2009-2013.

The 90-minute debate got off to a chilly start when the two candidates for the Nov 8 election greeted each other without the traditional handshake. It quickly turned into an acrimonious discussion of a 2005 video that emerged on Friday in which Trump was heard using vulgar language and talking about groping women without consent.

Trump said he was embarrassed by the video but dismissed it as "locker room talk." President Bill Clinton had done worse to women, he said.

"Mine are words and his are action," said Trump, who appeared before the debate with women who have accused Bill Clinton of sexual misconduct. In the debate, Trump also accused Hillary Clinton of going on the attack against women who had alleged sexual misconduct by her husband, president from 1993-2001.

Hillary Clinton responded that Trump's comments showed he was unfit for the White House.

"He has said the video doesn't represent who he is but I think it's clear to anyone who heard it that it represents exactly who he is," Clinton said.