MYRTLE BEACH: Jon Huntsman, the former US ambassador to China, ended his struggling presidential bid Monday and called on Republicans to unite in support of frontrunner Mitt Romney.

“Today, I am suspending my campaign for the presidency. I believe it is now time for our party to unite around the candidate best equipped to defeat Barack Obama,” he told supporters in South Carolina days ahead of the GOP primary in the state.

“Despite our differences and the space between us on some of the issues, I believe that candidate is governor Mitt Romney.”Huntsman had been running in last place in the polls ahead of South Carolina's January 21 primary, and his moderate positions had failed to draw support in a race bitterly contested by conservatives.

A former governor of Utah and ambassador, Huntsman used his parting remarks to decry the harsh negative attacks that have characterized the Republican battle to find a candidate to go up against Obama, the Democratic incumbent, in November.

“At its core, the Republican Party is a party of ideas, but the current toxic form of our political discourse does not help our cause, and it's just one of the many reasons why the American people have lost trust in their elected leaders,” he said.

“Today I call on each campaign to cease attacking each other, and instead, talk directly to the American people about how our conservative ideas will create jobs, reduce our nation's debt, stabilize energy prices and provide a brighter future for our children and our grandchildren.”

His decision was unexpected, coming after Huntsman picked up a major newspaper endorsement in South Carolina, which votes this Saturday in a crucial contest that could all but seal the deal for Romney.

Still, he was expected to win only around five to six percent of the vote in the southern state. Huntsman's endorsement, while not a game-changer, is welcome news for fellow Mormon Romney, who took a hit over the weekend when leading Christian evangelicals meeting in Texas chose to support rival Rick Santorum.

That move was symptomatic of lingering doubts among staunch conservatives over Romney, who has flip-flopped on core issues such as gay marriage and abortion in the past, and whose Mormon faith is a problem for some.

That hurdle to Romney's nomination has come into sharper relief as the Republican race has moved out of the northern states into the Bible Belt, where religion and politics often make for a volatile mix.

Polls show Romney, who won both of the first two nominating states, Iowa and New Hampshire, with a narrow lead over former House speaker Newt Gingrich.

Huntsman, a fluent Chinese speaker, struggled to strike a chord with primary voters, failing to shrug off his perceived closeness to the man most Republicans are united in loathing: Obama.

At a dramatic campaign launch in June at the Statue of Liberty, he promised to lead a civil presidential campaign, saying of Obama: “He and I have a difference of opinion on how to help a country we both love.

“But the question each of us wants the voters to answer is who will be the better president, not who's the better American.”

On paper he should have shone, but the conservative governor of a well-run state and two-time ambassador with business experience may have misjudged a Republican electorate eager more for red-meat attacks on Obama than his own steady-as-she-goes approach.

The 51-year-old scion of one of America's wealthiest families, whose billionaire father pumped money into a “super PAC” supporting him, skipped the campaign in Iowa and finished a distance third in the New Hampshire primary, with around 17 percent of the vote.

His departure leaves a five-way race between Romney, Texas Representative Ron Paul, Santorum, Gingrich and Texas Governor Rick Perry.