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Former Arkansas Gov. Mike Huckabee speaks at the Des Moines Register Republican Presidential Debate in Johnston, Iowa on December 12, 2007. This debate is the last before the Iowa caucuses. (UPI Photo/Andrea Melendez/POOL)

DES MOINES, Iowa, Dec. 31 (UPI) -- Political invective ratcheted up Monday among Republican presidential nomination contenders in the run-up to Thursday's first-in-the-nation caucus in Iowa.

Former Arkansas Gov. Mike Huckabee's campaign launched a TV ad campaign Monday attacking former Massachusetts Gov. Mitt Romney in response to his ads criticizing Huckabee's record on immigration, crime and foreign policy, the Wall Street Journal reported.

A Mason-Dixon poll in Iowa showed Romney had 27 percent support compared with Huckabee's 23 percent before the country's first caucus contest on Thursday.

For the top three Democratic contenders, various polls also showed a tight race in Iowa among the top three contenders -- Sen. Hillary Clinton of New York, Sen. Barack Obama of Illinois and former Sen. John Edwards of North Carolina, the Journal said.

Iowa's caucuses are more than two weeks earlier than usual, while the country's second race in New Hampshire on Jan. 8 is nearly three weeks earlier than in 2004.