The senator from Vermont took around three-quarters of the Democratic vote in the states of Alaska and Washington, according to early results. Sanders also defeated Clinton in Saturday’s Hawaii "presidential preference poll," the local name for the Democratic caucus.

Sanders swept all three states to give his campaign a much-needed boost against Clinton, who holds a commanding lead in the critical delegate count.

The former secretary of state had 1,223 delegates to Sanders' 920 going into Saturday's caucuses. But when superdelegates - party officials with the ability to vote for either candidate - are included, Clinton enjoys a 1,692 to 949 lead. It takes 2,383 delegates to secure the nomination.

The wide margin of victory on Saturday highlights divisions within the Democratic Party ahead of this summer's party convention to select the candidate for the November presidential election.

Speaking in Wisconsin, Sanders billed Saturday's victories as a Western comeback, one that would give renewed impetus to his campaign.

"We knew from day one that we were going to have politically a hard time in the South," he told a crowd. "That is a conservative part of our country. But we knew things were going to improve as we headed west."

A self-declared democratic socialist, Sanders continues to draw large crowds to rallies and is especially popular among younger voters, tromping Clinton in the critical electorate that twice brought President Barack Obama to the White House.

He has done well in states with larger white populations and where caucuses are held, due to the outsized role liberal Democrats can play in those contests.

Unlike Republicans, which have a winner-take-all system to allot delegates, Democrats allocate delegates based on a proportional system, meaning that even the loser in a state can still pick up delegates.

On Tuesday, Sanders won caucuses in Utah and Idaho but lost to Clinton in Arizona, a state with more delegates.

The next Democratic caucuses are on April 5 in Wisconsin, April 9 in Wyoming and April 19 in New York, where Clinton served as a senator.

New York is followed a week later by five northeastern states.