Billionaire US businessman Donald Trump has endorsed front-runner Mitt Romney for the Republican Party's presidential nomination.
Mr Trump announced his support at a Las Vegas hotel he owns, contradicting earlier reports that he would back Romney rival Newt Gingrich.
The candidates have been campaigning in Nevada after Mr Romney's resounding win in Florida's primary on Tuesday.
The eventual nominee will go on to face Barack Obama in November's election.
Telling Romney supporters that it was his honour to endorse the former Massachusetts governor, Mr Trump said foreign business people he deals with had taken advantage of increased US uncompetitiveness.
In short remarks, Mr Trump said Mr Romney would not "allow bad things to continue to happen to this country we all love".
Aides from the office of Mr Trump and Republican officials told US media that the real estate tycoon and reality TV star had spoken to Mr Romney on Wednesday night to inform him of the endorsement.
The outspoken businessman flirted last year with the idea of jumping into the presidential race himself as a third-party candidate, but ultimately decided not to.
Mr Trump said on Wednesday that he had an announcement to make about the presidential race, but did not say what it was. US media then reported that he would endorse Mr Gingrich.
Former House of Representatives Speaker Mr Gingrich told reporters he had not spoken to Mr Trump for weeks and was not aware of any plans by the businessman to back a candidate.
In an interview with ABC News on Monday, Mr Trump said he was still undecided as to whether to support Mr Romney or Mr Gingrich.
"I like both," Mr Trump said. "They both want my endorsement. We'll see what happens but in a very short time I'll be making an endorsement."
On Thursday, the candidates were campaigning in the south-western state of Nevada ahead of its Republican caucuses on Saturday.
An opinion poll released by the Las Vegas Review-Journal on Thursday showed Mr Romney, a former Massachusetts governor, leading the pack by 20 percentage points.
He was on 45%, while Mr Gingrich was on 25%, former Pennsylvania Senator Rick Santorum 11% and Texas Congressman Ron Paul 9%.
The Trump development may at least give Mr Romney's campaign some respite from negative publicity over ill-chosen remarks he made about the poor on Wednesday morning.
During an interview with CNN, the private equity tycoon said: "I'm not concerned about the very poor. We have a safety net there. If it needs repair, I'll fix it. I'm not concerned about the very rich. They're doing just fine. I'm concerned about the very heart of America, the 90-95% of Americans who are struggling."
Mr Gingrich led critics in pouncing on his rival's remarks about the poor, in an attempt to portray him as out of touch with the lives of ordinary voters.
At a rally on Thursday, the former House Speaker said "we should care about the very poor" unlike Mr Obama or Mr Romney.
Mr Romney later told reporters on his plane: "Of course I'm concerned about all Americans... poor, wealthy, middle class, but the focus of my effort will be on middle-income families who I think have been most hurt by the Obama economy."
Nevada's caucuses on Saturday are the next contest in the state-by-state process of picking a Republican nominee to challenge Democratic President Barack Obama in 6 November's general election.
The Silver State offers 28 delegates, out of 1,144 needed to clinch the nomination at August's Republican convention.