After his razor-thin victory in Iowa, former Massachusetts Governor Mitt Romney on Wednesday predicted fast and furious attacks from rivals seeking to oust him from his front-runner perch in the race for the Republican presidential nomination.

Romney edged out Rick Santorum, a conservative former Pennsylvania senator, by only eight votes in Iowa's caucuses, the first presidential nominating contest of 2012, as each received about 25 percent of the vote.

Ron Paul, a Texas congressman known for his small-government views, was a close third with just over 21 percent.

The field of candidates seemed likely to narrow after the Iowa result after two of the seven leading contenders cancelled trips to South Carolina to reassess their campaigns.

U.S. Representative Michele Bachmann, who finished a disappointing sixth in Iowa with just 5 percent of the vote, cancelled events in the southern state and scheduled a news conference for 11 a.m. EST (4 p.m. British time).

Bachmann, a strong social and fiscal conservative, had focused her campaigning in Iowa after winning the Ames Straw poll there in August.

Texas Governor Rick Perry, who finished fifth in Iowa with just over 10 percent support, said he was going home to Texas to reassess his campaign.

New Hampshire holds its primary on January 10. South Carolina's is set for January 21, followed by Florida on January 31.

The Iowa result boosted Romney's status as the person to beat in the race to pick a challenger to President Barack Obama in November's election.

He had not been expected to do well in the midwestern state, where conservative Christian voters are a major influence on Republican politics. But Romney's eight-vote win over Santorum underscored his inability to secure the trust of socially and fiscally conservative Republicans ahead of what is likely to be the most expensive presidential election campaign in history.

Newt Gingrich, a former front-runner who finished in fourth place in Iowa at about 13 percent, signalled that he would campaign more aggressively against Romney, whom he has linked to a series of bruising TV attack ads.

I know the attacks are going to come and they're going to become more fast and furious now, Romney said on ABC's Good Morning America on Wednesday, after eking out his 30,015 to 30,007 win over Santorum.

Gingrich called Romney a liar on Tuesday and Santorum took a stab at him as a moderate, a dirty word to many conservative Republicans.

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Santorum, who until recently had been little more than an afterthought in the race, was the latest in a series of candidates to benefit from Romney's weakness. Perry and Bachmann had also been in the top-tier last year.

Campaigning in all of Iowa's 99 counties, he emphasized his home-schooled children and opposition to gay marriage in a bid for support from the rural midwestern state's large bloc of Christian conservatives.

Bachmann had also targeted Christian conservatives and focused her campaigning in Iowa, but her support seemed to shift to Santorum as the caucuses neared.

Santorum staked his campaign on a strong showing in Iowa, but with little cash and a bare-bones campaign operation he could have difficulty competing in other states.

Romney attributed his 25 percent share of the caucus vote to the large size of the field. This was a seven-person field, of course, and so you can't do with seven people in the field what you can do with a smaller field, he said on ABC on Wednesday.

Romney is a strong front-runner in New Hampshire. A Suffolk University poll on Wednesday had Romney at 43 percent, to 14 percent for Paul and 9 percent for former Utah Governor Jon Huntsman, who has based his campaign in the small New England State.

The Suffolk poll had Gingrich at just 7 percent and Santorum at 6 percent in New Hampshire.

With deep reserves of cash and a strong campaign infrastructure, Romney has the resources to compete in bigger states like Florida at the end of the month. He has been focusing his attacks on what he terms Obama's failed presidency.

A Republican official said Senator John McCain, the party's 2008 nominee, would endorse Romney on Wednesday.

Sparsely populated Iowa yields just 25 delegates of the 1,143 needed to lock up the Republican presidential nomination, and those delegates are not actually awarded for months after Tuesday's caucuses.

About 120,000 people participated in Tuesday's Republican vote, and another 25,000 participated in the Democratic caucus -- about 8 percent of the state's eligible voters.

(Additional reporting by David Morgan and Susan Heavey in Washington and Jane Sutton, Eric Johnson and Steve Holland in Iowa, Writing by Patricia Zengerle, Editing by Vicki Allen and Jackie Frank)

(This story was corrected in paragraph 8 to change the date of New Hampshire primary)