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.

bbc.com