US Democrats Hillary Clinton and Bernie Sanders now turn their attention to the final stretch of the nominating contest after each picked up wins on Tuesday as they vie to represent their party in the November race for the White House.

The Democratic primary - which has stretched longer than most anticipated - hits a slow period until June 7, when the final contests will be held, including the delegate heavy states of California and New Jersey.

The divided outcome on Tuesday in Kentucky and Oregon means Clinton won't yet be able to turn all of her attention to the general election and taking on presumptive Republican nominee Donald Trump, who locked up his party's nomination after the rest of his rivals dropped out in early May.

Clinton narrowly defeated Sanders in Kentucky, a state where she was not expected to be victorious. Sanders bested her in Oregon, a state that played to his strengths.

In Kentucky, the two candidates will likely split the 55 delegates up for grabs. In Oregon, Sanders will take only a handful more of the 61 delegates that were awarded.

Clinton's lead in delegates means it is likely she will eventually be her party's nominee, but she remains more than 100 delegates short of sealing the deal.

Trump has begun to organise his general election campaign. On Tuesday, he signed a joint fundraising agreement with the Republican National Committee. The agreement allows him to raise $449,400 from a single donor by splitting the funds between his campaign, the RNC and state Republican parties.

Trump, who eschewed donations in the political system through the primary, has thus far insisted on mostly self-funding his campaign. The shift to a more traditional fundraising approach could draw ire from some of his supporters.

Trump, in an interview with Megyn Kelly that aired on Fox News Tuesday night, said he did have regrets about his actions during the Republican primary process.

"I could have used different language in a couple of instances, but overall I'm happy with the outcome," Trump said.

Nevada still rankles

Both candidates camps continued to exchange words on Tuesday after violent outbursts by Sanders supporters ended the Nevada Democratic convention.

Sanders supporters became angry when Nevada state party officials chose to end their convention and block efforts to award the US senator from Vermont more delegates than he initially won in the February caucus. Clinton won the caucus.

One Sanders supporter threw a chair. Others applied chalk graffiti to a party building. Sanders supporters began circulating a picture of the party chairwoman Roberta Lange on the internet that included her cellphone number and encouraged others to contact her to express their unhappiness.

Lange said she's received several death threats, including to her husband and grandson. One voicemail left on her cellphone said "people like you should be hung in a public execution."

Sanders - who said he condemns violence and personal harassment of individuals - levelled some of the same complaints his supporters did, arguing that state party Chairwoman Roberta Lange did not allow a headcount on a disputed rules change. He also argued that 64 delegates to the state convention were not given a hearing before being ruled ineligible.

The state party disputed the Sanders campaign's interpretation of the events. It said some delegates did not show up at the convention and others were disqualified because they were not registered as Democrats in time.

In the wake of the dispute in Nevada, that involved a fight about allowing participation by Sanders supporters who didn't register to be Democrats in time, the Vermont senator increased his call to for the party to allow participation by non-party members. Sanders, a self-described democratic socialists, is not a registered Democrat.

"The Democratic Party is going to have to make a very, very profound and important decision. It can do the right thing and open its doors and welcome into the party people who are prepared to fight for real economic and social change," Sanders said at a rally in California.

Clinton's campaign continued to express confidence that she will be able to unify the party.

"Hillary Clinton is grateful to the thousands of Nevadans who came out to participate in the caucuses and convention process," Clinton campaign manager Robby Mook said in response to Nevada. "She believes every voice should be heard and no one should be intimidated, harassed or threatened in this process. When the primary process is complete, our party must come together and ensure a Democrat is elected to serve as our next president."