Republican front-runner George W Bush has decisively defeated John McCain in the South Carolina primary, putting his campaign for the party's presidential nomination back on track.

With results in from 99% of the state's precincts, Mr Bush had 53% of the vote, compared with 42% for his main rival. The only other contender, conservative talkshow host Alan Keyes, won only about 5% of the vote.

"Not only did we win, but we did so in a convincing fashion," said a triumphant Mr Bush after learning of his victory.

"This is a big victory. It confounded many of the people who were watching me campaign."

Mr McCain, in a hard-hitting concession speech, vowed to keep fighting against what he called Mr Bush's negativity.

About 600,000 people are thought to have voted - more than double the figure last time in 1996 - confounding the pre-primary analysis that a large turnout would help Mr McCain.

Make or break

Political analysts had said it was vital for Mr Bush to win the South Carolina primary if he was to regain momentum for the big states that lie ahead.

Had he lost, rank-and-file Republicans around the country, as well as some of his establishment supporters, might well have abandoned him.

But our correspondent says Mr Bush benefited in South Carolina from the backing of the state's party leaders, who offered not only their endorsements but organisational support.

He now has 46 of the 1,034 delegates needed to win the Republican nomination, while Senator McCain, who triumphed in New Hampshire, has 11.

Exit polls showed that the Texas governor owed his victory to the overwhelming support of Christian conservatives, who backed him by a three-to-one margin.

Now Mr McCain, a former Vietnam veteran, has only three days to regroup before Tuesday, when primaries take place in his home state of Arizona and, more importantly, in Michigan - the first major industrial state to vote in the 2000 campaign.

"You don't have to win every skirmish to win a war or a crusade and, though we fell a little short tonight, our crusade grows stronger," he told supporters in his concession speech. "I can't wait for the next round."

He pledged to keep pressing his message of campaign finance reform and fighting to kick big money interests out of American politics.

Off to Michigan

Mr McCain's campaign manager, who conceded defeat even before the polls closed, called the result "a bump in the road".

"If it were not for the massive negative campaign run against us, primarily in the religious conservative community, we would have carried the state," Rick Davis said.

The battle waged between the two candidates was bitter.

Mr Bush enlisted the full weight of the conservative establishment to blacken his rival's reputation and drive down his support among Democrats and independents, who were allowed to vote under the state's open primary rules

The two candidates for the Democratic nomination, Al Gore and Bill Bradley, were not in Saturday's ballot. The next big test for the Democrats is on 7 March - so-called Super Tuesday.

Both Republican candidates were heading straight to Michigan late on Saturday night.

Polls taken there before the South Carolina result were indicating a virtual dead heat.