WASHINGTON (AFP) - Bernie Sanders soundly defeated Hillary Clinton in Utah's Democratic caucuses late Tuesday (March 23), bringing his campaign a much-needed boost as he seeks to disrupt Clinton's path to the party's presidential nomination.

US networks projected Sanders was headed to a comprehensive victory in the western state, leading his rival by a whopping 50 percentage points in early results.

It was his first victory in the long nominations race since March 8, when the self-proclaimed democratic socialist won Michigan.

"Thank you to all those who caucused tonight in Utah!" Sanders posted on Twitter.

Earlier Tuesday Clinton easily defeated him in neighboring Arizona, a larger state with 75 pledged delegates at stake and where a substantial Hispanic population helped her secure victory.

Utah, whose population is more Caucasian, has 33 delegates up for grabs.

Democrats were also voting Tuesday in a third western state, Idaho, where 23 of the party's delegates are in play. Should the unyielding Sanders fare well there, as expected, he could emerge even with or even slightly ahead of Clinton in the delegate count for the night.

But it will do little to significantly slow Clinton's march to the magic number of 2,383 delegates needed to secure the Democratic nomination outright.

Prior to Tuesday's votes, the former secretary of state had amassed 1,656 delegates compared to 877 for Sanders.

Republicans held votes Tuesday too, with front runner Donald Trump winning in Arizona in a key winner-take-all state, and his chief rival Ted Cruz well ahead in early results in Utah, where he needs to secure more than 50 per cent of the vote to secure all the state's delegates.

Republicans were also caucusing in the Pacific territory of American Samoa.