The Republican presidential candidates were focussed on the southern U.S. states of Alabama and Mississippi Tuesday as voters in those conservative strongholds head to the polls.
Opinion surveys showed a nearly three-way tie in both states between frontrunner Mitt Romney, 65, and conservative rivals Rick Santorum, 53, and Newt Gingrich, 68.
The Pacific state of Hawaii and the territory of American Samoa also are to hold Republican Party caucuses on Tuesday, but the candidates have not campaigned there. Results will be available after 0000 GMT Wednesday.
Public Policy Polling surveys showed Mr. Gingrich with the lead in Mississippi and Romney with a slight edge in Alabama, though the three top candidates are nearly within the margin of error in each survey.
The southern states would seem to favour Mr. Santorum and Mr. Gingrich with their more socially conservative voters, but the two candidates appear to be splitting the vote and giving Mr. Romney an opening.
The Republican Party is strongly entrenched in the south and Mr. Romney has struggled to connect with awkward references to regional cuisine and his years as governor of the northern state of Massachusetts.
But Mr. Santorum, who has emphasized his socially conservative positions on issues such as abortion and working-class roots, is also from the north, where he represented the state of Pennsylvania in the U.S. Senate.
Only Mr. Gingrich has a home-field advantage, and the primaries could be particularly crucial for him. He has won votes in just two states, including most recently his neighbouring home state of Georgia last week. His campaign had indicated he needed to win this week to continue in the race, but Mr. Gingrich himself has backed off that position and vowed to remain in the race until the August party convention.
Mr. Santorum won by a landslide in the central U.S. state of Kansas Saturday in the State-by-State battle for the party’s nomination, adding fuel to his position that he is the party’s best conservative to face President Barack Obama in November elections.
He emerged as the chief challenger to the more-moderate Romney after narrowly winning the initial contest in Iowa in January and picking up victories in six more states.
On Super Tuesday last week, Mr. Romney, who turned 65 Monday, maintained his lead for the party nomination and won six out of 10 contests.
Mr. Romney’s campaign has argued no opponent can catch him in the count for the convention delegates. Mr. Santorum and Mr. Gingrich continue to attack Mr. Romney as too moderate to represent the centre-right party.
The primary contests do not directly elect a nominee but allocate delegates to the candidates for the August convention, where 1,144 votes are needed to secure the nomination.