Democratic presidential candidate Hillary Clinton addresses the Planned Parenthood Action Fund in Washington, US, June 10, 2016. [Photo/Agencies]

WASHINGTON - Democrat Hillary Clinton won the District of Columbia primary on Tuesday, CNN projected on Twitter, capturing the party's last presidential nominating contest as Democrats turn their focus to the Nov 8 election against presumptive Republican nominee Donald Trump.

Clinton, who secured enough delegates to clinch the Democratic presidential nomination last week, will meet in private later on Tuesday with rival Bernie Sanders as the sometimes bitter political combatants search for common ground in the race against Trump.

Sanders is under pressure to give up his campaign and help unite the party. But the US senator from Vermont has vowed to push on to next month's convention to gain more converts to his agenda of reducing income inequality, curbing big money in politics and reining in Wall Street.

At a news conference in Washington on Tuesday, Sanders said he would also demand changes to make the Democratic nominating process more equitable, including replacing the Democratic National Committee leadership, letting independents take part in the voting and eliminating superdelegates, who are unelected and are free to support any candidate.

"The time is long overdue for a fundamental transformation of the Democratic Party," Sanders told reporters.

Sanders had promised to stay in the Democratic race until the final vote was cast in the Washington, primary, although he has stopped talking about capturing the party's nomination and instead focused on ways he can push his agenda.

He scheduled a national video address to supporters on Thursday night.