Bernie Sanders to work with Hillary Clinton

Democratic presidential candidate Bernie Sanders says in an address to his supporters that he will work with Hillary Clinton to transform the Democratic Party, adding that his "political revolution" must continue and ensure the defeat of Republican Donald Trump.

Sanders said in a capstone address to his political followers online that the major task they face is to "make certain" Trump is defeated.

The Vermont senator said he plans to begin his role in that process "in a very short period of time".

"But defeating Donald Trump cannot be our only goal. We must continue our grassroots efforts to create the America that we know we can become," Sanders said in remarks prepared for delivery on Thursday.

"And we must take that energy into the Democratic National Convention on July 25 in Philadelphia. where we will have more than 1900 delegates."

Sanders spoke from his Vermont hometown a week after Hillary Clinton secured enough pledged delegates and superdelegates to become the presumptive nominee.

He has not yet conceded the race or referred to Clinton as the likely nominee. But the two rivals met on Tuesday night in a Washington DC hotel along with advisers to discuss policy goals and future plans.

In the speech, Sanders thanked his supporters for providing more than $US200 million ($A271.39 million) in donations, most in increments of $US27, and rattled off the work of his loyalists: 1.5 million people who attended his rallies and town meetings and more than 75 million phone calls from volunteers "urging their fellow citizens into action".