During a rollicking 90-minute debate, US presidential candidates Hillary Clinton and Donald Trump traded barbs on a host of issues. Some of the most remarkable attacks came from Trump, who stated that he knew "nothing about Russia" and that he would jail his Democratic opponent if he were to be elected. 

Trump's jail comment came as part of his attack against Clinton over her use of a private email server while secretary of state and her transmission of eight emails labeled top secret.

Clinton, again, apologized for her use of the private server and added that there was no indication that any of the classified emails she sent had been seen by outside sources.

"That was a mistake and I take responsibility for using a personal email account. I am not making any excuses," she said.

But Trump was not satisfied and launched his attack.

"I think the thing you should really be apologizing for is the 33,000 emails you deleted and acid washed," he said. "If I win, I am going to instruct a special prosecutor to look into your situation.

Trump added that if he is elected president she would "be in jail."

Trump stiffs his running-mate

Another extraordinary moment came when the candidates discussed the humanitarian crisis in war-torn Syria. Trump admitted to a major policy disagreement with vice-presidential running mate Mike Pence. 

When asked about recent comments made by Pence that the US should consider airstrikes of its own in Syria, Trump flatly rejected the idea: "He and I haven't spoken and I disagree."

In recent days, Trump has faced numerous calls to renounce his candidacy and has lost the endorsements of many top Republicans over crude comments he made 11 years ago about groping and sexually assaulting women. Trump again tried to explain away his comments as mere "locker room talk."

"I have great respect for women, no one has more respect for women than I do," Trump said. "That was locker room talk as I told you. I am not proud of it."

Trump was responding to an audio tape that was published the Washington Post last week, in which he talked about kissing women and assaulting them by grabbing their genitalia, all without their consent.

In one of Clinton's strongest moments during the debate, she allowed that Trump's comments might be forgivable if it were a one-off occurrence. But she then reeled off a pattern of offensive behavior and comments made by Trump over the years, including during the past 18 months since he first announced his bid for the presidency.

She pointed out that Trump has insulted women, African-Americans, immigrants, people with disabilities and others, and concluded, "It's clear to anyone who heard (the audio tape), it represents exactly who he is."