US presidential front-runners, Democrat Hillary Clinton and Republican Donald Trump, have continued to dominate the race, winning Arizona.
The issue of immigration loomed large in the south-western state, the biggest prize in the latest round of contests.
Exit polls showed that Mr Trump’s anti-immigration message resonated with the state’s conservative voters.
With Arizona’s growing Latino population, Mrs Clinton continued her success by courting minority voters.
Although results were not yet available, Democrat Bernie Sanders was expected to win caucuses in two smaller states, Idaho and Utah.
Texas Senator Ted Cruz was also favoured to win the Republican caucuses in Utah.
Turnout was heavy on Tuesday with voters waiting in long queues in all three states holding contests.
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One Democratic caucus site in Boise, Idaho, reported more than 12,000 voters turned out.
The Republican primary in Arizona was a winner-take-all race, adding 58 delegates to Mr Trump’s sizable lead.
The property tycoon’s win complicates efforts by Mr Cruz and Ohio Governor John Kasich to stop him from securing a majority of delegates.
If Mr Trump falls short in the delegate count, the party could hold a brokered or contested convention where party leaders, not voters, choose the nominee.
However, that scenario is looking less likely as Mr Trump continues to win states.
As the final voters headed to the polls on Tuesday, the Republican race took another nasty turn.
Mistakenly believing the Cruz campaign had produced an attack advert about his wife Melania, Mr Trump on Twitter threatened to “spill the beans” on Mr Cruz’s wife, Heidi.
Mr Cruz responded saying his campaign did not produce the advert, calling Mr Trump “classless” and a “coward”.