WASHINGTON - US Republican presidential candidate Jon Huntsman announced Monday that he is dropping out of the race for the GOP nomination and endorsing his one-time rival Mitt Romney.

US Republican presidential candidate and former Utah Governor Jon Huntsman (L) pauses as he speaks at the Myrtle Beach Convention Center in Myrtle Beach, South Carolina January 16, 2012. [Photo/Agencies]

The former Utah governor and former US ambassador to China made the announcement at a press conference in Myrtle Beach, South Carolina, less than a week before the first-in-the-south primary takes place in the state.

"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 said. "Despite our differences and the space between us on some of the issues, I believe that candidate is governor Mitt Romney."

Rather than restoring bold and principled leadership, this campaign generated onslaught with personal and negative attacks against each other, he said, calling for campaigns that "cease attacking each other" and "talk to the American people."

Huntsman had mostly failed to gain traction in this election season, staying at the bottom of the pack in major national polls. He skipped the Iowa caucuses early this month and staked his candidacy almost entirely on a strong showing in the first-in-the- nation primary in New Hampshire last week.

However, a third-place finish in the New Hampshire primary failed to bring the momentum he needed to keep his campaign going. He did not receive a significant boost out of New Hampshire, as seen in the case for former Pennsylvania Senator Rick Santorum after a strong showing in Iowa.

Huntsman, 51, distinguishes from the rest of the field with significant foreign policy experiences. He served in diplomatic positions during the two Bush administrations and as ambassador to China under President Barack Obama.

He is a moderate, which works against him in the conservative- dominated Republican primaries. He also faces challenges from his Morman faith and experience of working for a Democratic president.

Huntsman's dropping out and endorsement will be a boost for Romney, the former Massachusetts governor, as the two candidates have been competing for a similar pool of GOP primary voters -- Republican moderates.

Romney claimed back-to-back victories in both Iowa and New Hampshire. He currently leads in South Carolina in major polls though not with significant margin. If he wins South Carolina, said analysts, it would be extremely difficult for any of his Republican fellows to stop him from winning the nomination.