Democratic presidential hopefuls Hillary Clinton and Bernie Sanders have sparred over who is more committed to US immigration reform at a presidential debate in Miami.

Debating on Wednesday evening, a few days before Florida's crucial primary election, both candidates promised they would not deport undocumented immigrants without criminal records.

Clinton and Sanders took turns thrashing Republican frontrunner Donald Trump for his vow to round up and kick out millions of undocumented immigrants, with Clinton accusing him of "trafficking in paranoia".


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"I think the American people are never going to elect a president who insults Mexicans, who insults Muslims, who insults women, who insults African-Americans," Sanders said.

Earlier on Wednesday, Republican leaders opposed to Trump becoming the party's presidential candidate in the November US election warned that the billionaire businessman could become unstoppable if he wins two crucial nominating contests next week.

Mexico border wall

Clinton got some laughs by saying that Trump wants to build "a beautiful, tall wall" that will "magically" be paid for by the Mexican government.

Her comments came in response to a question on whether her vote as a New York senator to build a wall on the southern border differs from Trump's plan, which she has called ridiculous.

Clinton said responsible legislators chose to improve border security with more agents and some fencing when needed, and as a result the country has lower rates of illegal immigration.

Once again Clinton defended her role in the deadly 2012 attack on the American mission in Benghazi, Libya.

She said at Wednesday's debate that her shifting explanations for the crisis in the early hours were because of changing dynamics and new information.

Clinton also said the investigation has been politicised by Republicans seeking to score points against her campaign.

"This was fog of war," she said, saying that she regrets the lives lost in the crisis. She added: "I wish there could be an easy answer at the time but we learned a lot."

Sanders boasted at the debate that his upset win in Michigan's primary the day before over Clinton had rejuvenated his campaign.

Sanders pointed out that some observers considered the victory, which was not forecast by opinion polls, "one of the major political upsets in modern American history", saying the win strengthened his case for being the party's nominee.

The senator from Vermont said the task before him was to convince the so-called Democratic "superdelegates," party elites who have largely sided with Clinton, that he "is the strongest candidate to defeat Donald Trump," Sanders said.

Asked about the Michigan loss, Clinton said. "It was a close race. I've won some. I've lost some."

Source: Agencies