Hillary Clinton has brought a close to the presidential primary season with a win in the nation's capital and a meeting with beaten rival Bernie Sanders.

The talks in Washington DC were aimed at setting a tone of Democratic unity heading into next month's party convention in Philadelphia.

Ms Clinton's win in the final primary of the year had no bearing on her role as the presumptive nominee, but it marked a transition in the lengthy primary fight between the two rivals.

In virtually identical statements released after meeting for more than 90 minutes, the Clinton and Sanders campaigns said the rivals discussed their primary campaign, "unifying the party and ... the dangerous threat that Donald Trump poses to our nation".

Ms Clinton told Mr Sanders she appreciated his commitment to stopping Mr Trump in the general election and the two discussed issues in which they share common goals, including "raising wages for working families, eliminating undisclosed money in politics and reducing the cost of college for students and their families".

Both candidates agreed to work together on the development of the platform at the upcoming Democratic National Convention.

Before polls closed in Washington, Mr Sanders vowed again to do all he can to prevent Mr Trump, the presumptive Republican presidential nominee, from reaching the White House - but he declined to endorse Ms Clinton.

The Vermont senator had said the private meeting would help him determine how committed Ms Clinton will be to the policy issues he has staked out during his 13-month campaign.

"Our goal must not be to allow politicians, Donald Trump or anyone else to divide us," he said outside his Washington headquarters, telling reporters he will continue to "fight as hard as we can" to transform the Democratic Party.

Mr Sanders said he would push for new leadership in the Democratic National Committee along with a progressive platform in the summer convention and electoral changes, such as primaries that allow independents to participate and the elimination of superdelegates.

"We need major, major changes in the Democratic Party," he said.

Mr Sanders last week met President Barack Obama and vice president Joe Biden, who both later endorsed Ms Clinton, and signalled to Democrats that he hopes to play a constructive role in helping the party regain control of the Senate in the 2016 elections.