|Gingrich, right, said Romney's attacks were riddled with falsehoods and his rival was not "telling the truth" [Reuters]
US Republican presidential candidates, Mitt Romney and Newt Gingrich, have clashed in a bitter debate days ahead of the Florida primary in which both are vying for front-runner status in the battle to challenge Barack Obama in November.
A newly aggressive Romney on Monday charged that Gingrich had "resigned in disgrace" from Congress after four years as House speaker, and subsequently worked as an "influence peddler" in Washington.
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"In the 15 years after he left the speakership, the speaker has been working as an influence peddler in Washington," said the former Massachusetts governor. "I think this is going to come down to a question of leadership."
Gingrich shot back at his rival, saying Romney's attacks were riddled with falsehoods and that his rival was not "telling the truth".
"I don't want to waste any time on it," he said, "It is the worst kind of trivial politics".
The clash occurred in the opening moments of the first of this week's two debates before the January 31 Florida primary in which Gingrich, who won in South Carolina last week, has taken a lead over Romney, according to two new polls.
On his Iran policy, Romney said he would consider it an "act of war" if Iran was to shut down the Strait of Hormuz, a key transit route for global oil supplies.
"We want to show Iran" that closing the Strait or any similar act, Romney said, "will be considered an act of war, an act of terror and America is going to keep the sea lanes open".
In the lead-up to the debate, Romney called on Gingrich to release his contract with Freddie Mac, the mortgage giant blamed for helping to cover up the depth of America's housing bubble which collapsed plunging the nation into recession, hitting Florida particularly hard.
Gingrich, who was paid some $1.6m in consulting fees for what he called his advice as a "historian" to the company, readily obliged, releasing his contract just hours before the debate.
Romney, a multimillionaire businessman once considered the presumptive nominee, has struggled to win over the Republicans' conservative base, which remains wary of his Mormon faith and his changing positions on key issues such as abortion and gay marriage.
For his part, Gingrich has tried to brush aside accusations of erratic, chaotic leadership in Congress when he was also hit by an ethics inquiry, as well as overcome questions over his marital infidelities.
US involvement in Cuba
As the two top Republican front-runners engaged in the heated debate, the other two Republicans still in the race, Christian conservative Rick Santorum and Texas congressman Ron Paul, paled into the background.
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Paul, who was trailing with just eight per cent support in Florida, said he would like to see the Cuban people celebrate their own freedom without any US involvement.
"I don't like the isolationism of not talking to people ... the Cold War is over. ... We talked to the Soviets. We talk to the Chinese. ... I don't know why the Cuban people should be so intimidating."
He also denied that he was planning to run as a third-party candidate.
Santorum, who stood at the third place with 11 per cent support, put questions for both Romney and Gingrich.
"My question to Governor Romney and to Speaker Gingrich, if you believe in capitalism that much, then why did you support the bailout of Wall Street, where you had an opportunity to allow destructive capitalism to work, to allow a failure of a system that needed to fail because people did things that in capitalism you pay a price?"
On Iran he said: "The bottom line is the theocracy that runs Iran is the equivalent of having al-Qaeda in charge of a country with huge oil reserves, gas reserves, and a nuclear weapon."