WASHINGTON — Republican White House hopeful Mitt Romney picked up the key endorsement of Mississippi Governor Phil Bryant, days ahead of a primary in the conservative southern state.

Bryant said on Thursday he thought Romney had the best chance of beating President Barack Obama in November's general election and believes the multimillionaire former businessman can "turn America around to get back on the right track."

In a radio interview in neighboring Alabama, which like Mississippi holds its primary on Tuesday, Romney, a former governor of liberal Massachusetts, said he considers the votes in the conservative south to be an "away game."

His closest rival for the Republican presidential nomination, Rick Santorum, a devout Catholic and socially conservative former US senator, is expected to connect strongly with voters in the American "bible-belt" region.

Romney has won 14 states to Santorum's seven and seems to be marching inexorably towards the crucial 1,144 delegates needed for the nomination.

The frontrunner has however struggled in the south, losing to Santorum in Tennessee and Oklahoma, and to former House speaker Newt Gingrich in South Carolina.

If Gingrich fails to win both Mississippi and Alabama on Tuesday he could be forced out of the race, having pinned his hopes of a resurgence on sweeping the South.