Republican presidential candidate Mitt Romney
Republican presidential candidate Mitt Romney greets supporters during a campaign stop in Kirkwood, Missouri. He is locked in a three-way fight for dominance as key Southern states vote.
White House hopefuls were locked in a close three-way fight Tuesday as they battled for dominance in key Southern states, which could bust open the unruly Republican presidential race.
Voters in the deeply conservative states of Alabama and Mississippi were going to the polls to choose their Republican candidate to stand against Democratic President Barack Obama in November elections.
Front-runner Mitt Romney aims to begin locking up the state-by-state nomination process while his top rival, ex-senator Rick Santorum, seeks to cement his status as the best alternative to the former Massachusetts governor.
But the race has been deadlocked for weeks, even as Romney inches ahead in the votes, and all eyes were on former House speaker Newt Gingrich who has branded Tuesday's contests as must-wins for his flagging campaign.
The flamboyant Gingrich, who in the early days of the campaign was denounced for what candidates called his "grandiose ideas," is fighting to remain viable after winning just two out of the 26 contests held so far. But he faces mounting calls to pull out and allow conservatives to coalesce around Santorum.
Under overcast skies, voters in Birmingham, Alabama, lined up waiting for the polls to open.
Unofficial early exit polls in suburban Shelby County, where many conservative Republicans live, showed voters were deeply divided, with the fourth contender, libertarian Congressman Ron Paul, not seen as playing well.
Lori Robertson, 47, voting on her way to work as a physical therapist and already dressed in her scrubs, said she threw her support behind Romney, in part because "he has a stronger chance to beat Barack Obama."
Roy Watkins, 65, chief executive at Cebert Pharmaceuticals, said he voted for devout Catholic and former Pennsylvania senator Santorum. "The values that he has represent me," he told AFP.
But 45-year-old insurance executive Troy Wolkow, his wife Mary, 46, and his 19-year-old daughter, Nicole, all said they had opted for Gingrich.
"I think he's the best candidate. His knowledge, his grasp of the issues and he's somebody that inspires me. If he becomes president, I see him as the most capable of being a leader," Troy Wolkow said.
In a sign that Santorum is perhaps preparing for defeat, he scheduled a Tuesday night rally in Louisiana, moving his campaign to the state which votes next week, a few days after Illinois.
Earlier polls predicted a tight race in the deep South, with Santorum perhaps losing out despite a weekend win in Kansas.
Public Policy Polling found Gingrich held a slight lead in Mississippi with 33 percent to 31 percent for Romney, and Santorum at 27 percent. In Alabama, the race is even closer with 31 percent for Romney, 30 percent for Gingrich and 29 percent for Santorum.
Hawaii was also holding a caucus to pick its nominee.
Gingrich, speaking to Fox News on Tuesday, dismissed Romney as the candidate of corporate fat cats and touted his plan to bring down the price of gas to $2.50 from around $4 currently.
"Barack Obama is responsible for the high price of gasoline. He has followed a deliberately anti-American energy policy," Gingrich said, tapping into anger about high prices at the pump which are hurting Obama's popularity.
But in pointed remarks, White House spokesman Jay Carney dismissed what he called a partisan campaign to misrepresent Obama's energy policy.
"The president on his watch over the past three years has taken significant actions to increase... domestic oil and gas production," Carney said.
Santorum has also trained his sights on Romney, saying the party needs a standard bearer in the mold of late conservative icon president Ronald Reagan.
Romney for his part has argued that he alone has the heft to beat Obama.
"It's essential that we have in Washington a president who understands how the free economy works... how free people pursuing their own dreams make a stronger nation. I've had that experience," he said at a Tuesday rally.
Romney is already ahead in the all-important delegate count, having about 40 percent of the 1,144 needed to win the sweepstakes and be crowned the party's presidential nominee at its convention in August.
But the Santorum campaign accused him of "fuzzy math."
"The reality is simple: the Romney math doesn't add up and he will have a very difficult time ever getting to a majority of the delegates," the Santorum campaign said in a memo, arguing "time is on our side."