Republican contest: Rick Santorum seeks Louisiana rebound
Voting is under way in the southern US state of Louisiana, in the latest round of polls to select the Republican party candidate to run for the White House.
Front-runner Mitt Romney is hoping to extend his lead, despite predictions of a strong performance by the closest challenger, Rick Santorum.
Mr Romney has so far won 21 out of 33 contests, most recently securing a decisive victory in Illinois.
The eventual nominee will challenge Barack Obama in November's election.
One-time favourite former House Speaker Newt Gingrich, now in third place, is struggling to reinvigorate his campaign, and Texan Ron Paul has yet to win a poll.
The Louisiana contest is expected to deliver a boost to Mr Santorum, who enjoys strong support among conservatives in the south, according to pre-poll surveys.
He has also picked up backing from Republicans who have peeled away from Mr Gingrich as he lost momentum.
However, a confident showing on Saturday by the former Pennsylvania senator could be illusory, correspondents say.
Mr Romney, an ex-Massachusetts governor, is widely tipped to regain the advantage when the race moves on in April to Wisconsin, Maryland and Washington DC.
He also received a boost earlier this week when he secured the endorsement of former Florida Governor Jeb Bush.
Mr Bushcalled on Republicansto "unite" behind the Romney campaign.
Correspondents say the backing of the respected Republican suggests the party establishment could be coalescing around Mr Romney.
In another boost, FreedomWorks, an organisation that supports the Tea Party movement, dropped its opposition to Mr Romney's candidacy.
Mr Romney has so far won 563 delegates versus Mr Santorum's 263, according to an estimate by the Associated Press news agency.
A candidate needs to accumulate 1,144 delegates to the August convention in order to secure the nomination.