Washington (AFP) - Hillary Clinton and Bernie Sanders clashed forcefully on the debate stage Wednesday, with the Democratic presidential rivals opening lines of attack on immigration in the aftermath of Sanders' stunning upset win in Michigan.

With their Miami debate showdown coming just six days before the critical Florida primary, the two candidates were repeatedly pressed on immigration issues, including whether they would deport undocumented children from the United States.

Both said they support comprehensive immigration reform and pathways to citizenship for many of the 11 million people living in the shadows.

In stark contrast, Republican candidates all say they want no such track to citizenship. Donald Trump, the Republican frontrunner, wants to deport millions.

But with Florida home to a large Hispanic community, frontrunner Clinton and her sole Democratic rival Sanders openly courted the Latino vote -- each quickly said they would not expel the children of illegal immigrants, or undocumented adults with no criminal records.

It marked a break, too, of sorts from President Barack Obama's administration, which has come under fire for its aggressive deportation policies.

"I would not deport children," Clinton said.

"My priorities are to deport violent criminals, terrorists and anyone who threatens our safety."

But she also wanted to "stop the raids, stop the round-ups, stop the deporting of people who are living here doing their lives, doing their jobs."

Sanders was more blunt on disagreeing with Obama. "He is wrong on this issue of deportation," Sanders said. "I disagree with him on that."

Clinton slammed Sanders, a self-described democratic socialist, for voting against an immigration reform bill in 2007.

But Sanders shot back that Clinton had taken anti-immigrant positions in the 2000s, such as prohibiting the issuing of driver's licenses to illegal immigrants.

They also clashed on the war in Iraq, Clinton's relationship with Wall Street and corporate America, health care policy and tuition for state universities.

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"Madame secretary, I will match my record against yours any day of the week," Sanders boomed.

- 'This is a marathon' -

The pair sharpened their attacks, with Sanders sensing momentum after a remarkable win 24 hours earlier in Michigan, where Clinton had been expected to prevail.

Clinton has nonetheless passed the half-way point in the race to the 2,383 delegates needed to win the party's presidential nomination, after she handily defeated Sanders in the southern Gulf state of Mississippi.

Yet the Vermont senator's upset win in Michigan raised questions about the former secretary of state's ability to win over key industrial states in the general election in November.

Clinton has won 13 out of 22 contests and despite the Michigan setback her team remain confident, explaining that her blowout win in Mississippi meant she walked away with the majority of Democratic delegates and is inching closer to an "insurmountable" delegate lead.

But Sanders has shown remarkable resilience and the intensity of the debate suggested Clinton was taking his challenge seriously.

"This is a marathon," Clinton acknowledged.

She faced probing questions about her use of a homebrew email server and private account when she was secretary of state.

Clinton reiterated she made a mistake but said she was "not concerned."

Asked whether she would drop out of the race if she is indicted over the scandal, she bristled.

"Oh for goodness... that is not going to happen. I am not even answering that question," Clinton said.

- 'Un-American' rhetoric -

Trump emerged strengthened by victories Tuesday in Michigan, Mississippi and Hawaii.

He has now won 15 of 24 races and looks to next week's primaries that could be crucial to his effort to seize his party's nomination since, on the Republican side, Florida, Ohio and Illinois are winner-take-all in the delegate race.

Tuesday's big loser was Florida Senator Marco Rubio. He has been seen by party luminaries as the best mainstream hope of derailing Trump, but he has performed dreadfully in several recent primary contests, including those Tuesday.

With his campaign appearing to be on the verge of fizzling, he was reflective when he spoke to MSNBC, saying he was "not entirely proud" of stooping to using dirty jokes or mocking Trump's appearance in recent weeks.

"My kids were embarrassed by it, and if I had to do it again I wouldn't," Rubio said.

He and Ohio Governor John Kasich face must-wins in their respective home states on March 15. Trump leads polls in those battlegrounds and he made clear he aims to snag them both.

"If I win those two I think it's over," Trump told CNN.

The New York real estate mogul's caustic style and incendiary rhetoric has angered some voters and influential Republicans, but he insists he can reunite the party and draw millions more to the polls.

"I think Islam hates us," Trump told CNN in an interview aired late Wednesday in the latest example of such overheated rhetoric.

Clinton attacked Trump's use of words as "un-American."

"I'm not going to engage in the kind of language that he uses," she said.

Republican white House hopefuls take to the debate stage Thursday night.