Democrats Abroad is the official arm of the Democratic Party for Americans living overseas, and voters in 180 countries cast their ballots in the primary. Sanders won 57.9% of the vote and 9 delegates, and former Vice President Joe Biden won 22.7% of the vote and 4 delegates.

Biden substantially expanded his delegate lead over Sanders with his sweep of all three of last Tuesday's Democratic primaries in Arizona, Illinois and Florida. After the losses, Sanders said he would assess his presidential campaign

As of Monday, Biden has a more than 300-delegate lead over Sanders, according to CNN's estimate.

Democrats Abroad said its primary saw the highest turnout in its history of presidential primaries and was up more than 15% from 2016. Countries with the highest turnout included the United Kingdom, Germany, Canada, France and Mexico, according to the group.

"Americans abroad are consistently a very blue voting bloc, and the turnout we've seen during the primary, as well as in voter turnout of general elections in 2016 and 2018, reflect that. Our voters believe in affordable healthcare and education, and a government that looks after its people -- both those citizens at home and abroad," said Amanda Mohar, the communications director for Democrats Abroad.

In 2016, Sanders won the primary, receiving 68.8% of the vote compared with Hillary Clinton's 30.9%.