Hillary Clinton moved to just under 30 delegates short of securing the Democratic Party's presidential nomination with a win in the US Caribbean territory of Puerto Rico on Sunday.
The victory, along with a win Saturday in the US Virgin Islands, places Clinton some 28 delegates short of the 2,383 she needs to seal the nomination, giving her momentum ahead of the final state primaries on Tuesday.
With almost 70 per cent of votes counted, Clinton was leading with 59.38 per cent of votes, ahead of Bernie Sanders at 37.53 per cent, according to the latest count by electoral officials.
"We just won Puerto Rico!" Clinton tweeted before thanking the "island of enchantment" in Spanish.
Puerto Rico awards 67 delegates, the majority of whom will be divided between the candidates based on the results of Sunday's contest. In the Virgin Islands, she won all seven delegates awarded.
Not all delegates from Puerto Rico had been awarded, but a tally kept by the New York Times gave Clinton 31 to Sanders' 16.
Voters in both Puerto Rico and the Virgin Islands can participate in party primaries to choose presidential candidates, but are not able to vote in the November general election.
Clinton has a sizeable lead over Sanders in the total number of delegates needed to win the party nomination at its July convention. Her lead is narrower without the party's so-called superdelegates, who can support whomever they choose and have so far overwhelmingly backed Clinton.
The last remaining states - New Jersey, North and South Dakota, Montana, New Mexico and California - will choose presidential delegates on Tuesday, with Clinton sure to win enough votes to secure the nomination.
Only reversals by hundreds of superdelegates ahead of the Democrats' convention next month in Philadelphia could keep her off the November general election ballot against presumptive Republican nominee Donald Trump.
Sanders hopes that a strong win in California, which is the largest prize on Tuesday, could prompt many superdelegates to reevaluate their support and perhaps force the nomination to be decided at the party convention.
The federal district of Washington DC holds the final Democratic primary on June 14.