Republican presidential candidate Donald Trump has easily won the US state of Nevada, cementing his lead in the race for party nomination.
The billionaire now has three consecutive wins, after victories in New Hampshire and South Carolina.
Senators Marco Rubio and Ted Cruz, who have been attacking each other this week, are vying for second place.
Party officials said they were looking into reports of double voting and not enough ballots at one caucus site.
Some volunteers also wore clothing in support of Mr Trump, but officials said this was not against the rules.
In his victory speech, Mr Trump told a roaring crowd of supporters: “We’re winning, winning, winning the country, and soon the country is going to start winning, winning, winning.”
Nevada, typically a swing state with a substantial Latino population, is crucial to the election process. Hillary Clinton won the state on Saturday in the Democratic race.
Some 30 delegates – around 1% of the total – are up for grabs in the Nevada caucuses, the first Republican test in the west of the United States.
With nearly 90% of the votes counted, Donald Trump has a 46% lead over the rest of the Republican pack, with his closest rival Marco Rubio getting 23%.
Cheers erupted at the Trump camp in Las Vegas as US networks started projecting his victory.
In the Democrats’ caucus in Nevada last week, Mrs Clinton beat rival Bernie Sanders by five percentage points. Next Saturday, both candidates face each other in South Carolina, where they are focusing their campaigns on the black vote.
The aim of the primary and caucus races in the coming months is to determine which candidates will stand for the two main parties in the November presidential election.
The Democrats and Republicans are now gearing up for the Super Tuesday round on 1 March – when about a dozen states choose their party candidates, with about a quarter of all nominating delegates up for grabs.
The billionaire from New York locked horns with Texas Senator Ted Cruz on Monday, attacking his campaign tactics and describing his rival as “sick”. It comes after Mr Cruz fired his campaign spokesman over a doctored video that discredited Senator Rubio’s views on the Bible.
Mr Cruz hit back on Tuesday, accusing Mr Trump of “vacillating” on his campaign issues and policies. Marco Rubio, meanwhile, has been urging registered Republicans to turn out in force for the caucuses.
“I need your vote tonight!” Mr Rubio, considered the preferred candidate among more moderate Republicans, told a rally on Tuesday.
Rivalry between Mr Cruz and Mr Rubio – both Latino senators – has also intensified in recent days, with both candidates attacking each other on the campaign trail.
Elsewhere, retired neurosurgeon Ben Carson, who is trailing the Republican pack alongside Ohio Governor John Kasich, hit the headlines after suggesting US President Barack Obama had been “raised white”.
For his part, John Kasich is focusing campaign efforts on the bigger states of Virginia and Michigan.
The caucuses, which began at 17:00 local time (01:00 GMT Wednesday) and lasted three hours, allow Republican supporters to hold an open discussion about their favourite candidates before they vote in a secret ballot.
The Republican field, which numbered a dozen one month ago, has been whittled down to five, after one-time establishment favourite Jeb Bush dropped out of the race in South Carolina last weekend.