Down but not out, Senator Bernie Sanders scored a big win in the Democrats Abroad global primary as the contest to become the party's candidate in November's US presidential election heats up.

"We are waging a strong campaign and plan to take it all the way to the Democratic National Convention this summer," Sanders said after his win on Monday.

The party said 34,570 American citizens living abroad in 38 countries cast votes by internet, mail, and in person from March 1 to 8.

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Sanders received 69 percent of the vote to earn nine of the 13 delegates at stake. Hillary Clinton won 31 percent, picking up four delegates.

It is an important victory for Sanders, who was beaten by Clinton in five states last Tuesday.

Still, Sanders continues to trail Clinton by more than 300 delegates.

Clinton now has 1,163 delegates to Sanders' 844 based on primaries and caucuses.

In the US primary system, voters select delegates supporting their candidates in each state and then the delegates vote for the candidates in parties' national conventions.

When including superdelegates, or party leaders who can support any candidate, her lead is even bigger - 1,630 to Sanders' 870. It takes 2,383 delegates to win the nomination.

Halfway into the primary season, the Democratic race now moves to western states this week that Sanders is counting on winning to cut into Clinton's lead.

On Tuesday, Democrats vote in Arizona, Idaho and Utah, with 131 delegates up for grabs; on Saturday, Alaska, Hawaii and Washington hold caucuses with 142 delegates at stake.

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Source: AP