Republican presidential candidates spar in TV debate
Republican front-runners Mitt Romney and Newt Gingrich have clashed at a debate in Florida, the last before the key state's primary.
The fiercest exchange came as former House Speaker Mr Gingrich repeated his charge that Mr Romney was the most anti-immigrant candidate.
The former Massachusetts governor aggressively fought back, labelling Mr Gingrich's claim "repulsive".
The candidates are vying to challenge Barack Obama for the White House.
Primaries and caucuses will be held in every US state to pick a Republican candidate until the eventual winner is anointed at the party's convention in August, before taking on the Democratic president in November's elections.
Mr Romney and Mr Gingrich are neck-and-neck in Florida's opinion polls following the latter's upset win in South Carolina's primary last week.
Former Pennsylvania Senator Rick Santorum and Texas Congressman Ron Paul are trailing, ahead of the Sunshine State's primary next Tuesday.
The stakes are high because a win in Florida has the potential to propel one of the contenders to the nomination.
Thursday's debate was the last time the candidates appeared together on a national stage ahead of the primary.
Immigration dominated the opening exchanges in a debate held in a state with a large immigrant - especially Latino - population.
Mr Romney said Mr Gingrich should apologise for running ads calling him an anti-immigrant candidate.
"The idea that I'm anti-immigrant is repulsive," Mr Romney said to audience cheers. "It's simply the kind of over-the-top rhetoric that's characterised American politics too long.
"I think you should apologise for it and recognise that having differences of opinions does not justify labelling people with highly charged epithets."
But the former House Speaker said his rival's immigration policy would result in the deportation of grandmothers who are in the country illegally.
Mr Gingrich's campaign withdrew a radio ad this week that made the anti-immigrant charge, after American-Cuban Florida Senator Marco Rubio called on him to do so.
Mr Paul said US dollars should be spent on securing the nation's border with Mexico, rather than in the Middle East.
Mr Romney also ridiculed Mr Gingrich's plans to establish a permanent base on the moon, an idea of interest to those on Florida's Space Coast.
Mr Romney said: "If I had a business executive come to me and say I want to spend a few hundred billion dollars to put a colony on the moon, I'd say, 'you're fired'."
Mr Gingrich raised questions about Mr Romney's wealth and his investments, saying: "I don't know of any American president who's had a Swiss bank account."
During a discussion about housing, the two front-runners also clashed over federal mortgage lenders Fannie Mae and Freddie Mac.
The former House Speaker said Mr Romney had been making money from investments in funds that were "foreclosing on Floridians".
Florida accounts for almost a quarter of home foreclosures in the US and the state's unemployment rate - at 9.9% - remains above the national average of 8.5%.
Mr Romney hit back that his rival, too, had invested in mutual funds with the two lenders, which many Republicans blame for the housing crisis.
Mr Santorum said the discussion was getting sidetracked with "petty personal politics".
He called for the candidates to focus on more substantive issues, asking the moderator: "Can we set aside that Newt was a member of Congress... and that Mitt Romney is a wealthy guy?"
Mr Romney, a wealthy businessman, has said his experience as the head of a private equity firm equips him to create jobs in the sluggish US economy. But many conservatives view him as too moderate and have misgivings about his Mormon faith.
He won a resounding victory in New Hampshire's primary, after a photo finish with Mr Santorum in Iowa's caucuses, the first nominating contest of the campaign.
Mr Romney later looked vulnerable to a resurgent Mr Gingrich, who was buoyed by brash performances in live debates.
However, doubts over the thrice-married former House Speaker's personal life and business dealings have also unsettled conservatives.