US Democratic presidential candidate Bernie Sanders has defeated Hillary Clinton in the West Virginia primary, slowing her march to the nomination.
Despite the setback, Mrs Clinton was still heavily favoured to become the Democratic candidate in the 8 November election.
But Tuesday's (local time) loss could signal trouble for Mrs Clinton with working-class voters in the US Rust Belt, where she would need to prevail in key states, such as Ohio and Pennsylvania, in the general election.
Mrs Clinton was put on the defensive in West Virginia because of comments she made during a town hall meeting in March.
Addressing environmental issues, she said she wanted put coal companies out of business.
Battered by dwindling demand and new environmental rules, coal companies are among the top employers in West Virginia.
Mrs Clinton later said she misspoke and that she wanted to bring new industries to the state.
During her visit to West Virginia and Ohio last week, she repeatedly apologised to displaced coal and steel workers for her comment, which she said had been taken out of context, and discussed her plan to help retrain coal workers for clean energy jobs.
Mr Sanders' message of economic fairness also resonated in West Virginia, one of the poorest states in the country.
While a win in West Virginia would not derail Mrs Clinton's path to the Democratic nomination, Mr Sanders' continued success would give him leverage to influence the party's platform.
"We're going to fight for the last vote," Mr Sanders said on Monday.
Mrs Clinton and Mr Sanders would compete in another primary contest on 17 May.
Both were also looking ahead to 7 June contests in which nearly 700 delegates would be at stake, including 475 in California, where Sanders was now focusing his efforts.
Mrs Clinton and Donald Trump were both already looking ahead to the general election.
The Nebraska and West Virginia primaries were the first since Mr Trump's last remaining rivals left the race last week.
Polls closed in West Virginia at 7.30pm EST (12.30pm NZT) and in Nebraska, where only the Republicans are voting, the polls close at 9pm EST (2pm NZT).
According to exit polls, the most important issue for voters in West Virginia was the economy and jobs.
Mr Trump, who won in West Virginia and Nebraska, was now trying to unite the Republican Party after a contentious primary season.
Many top Republican leaders, including House Speaker Paul Ryan, have declined to support Mr Trump's candidacy, saying the New York businessman did not represent conservative values.
Mr Trump would meet Senate Majority Leader Mitch McConnell and Mr Ryan on Thursday in hopes of resolving their differences.
Some Republicans were concerned that Mr Trump would negatively affect other races, hurting the party's chances of retaining control of Congress.
Mr Trump is deeply unpopular among key voting blocs including women, Latinos and African Americans.
He has taunted Mrs Clinton in recent days by saying she "can't close the deal" by beating Sanders, her only rival for the Democratic Party's nomination since 1 February.
For her part, Mrs Clinton, 68, said she would ignore Mr Trump's personal insults, including his repeated use of his new nickname for her, "Crooked Hillary," and instead would criticise his policy pronouncements.
To secure the Democratic nomination, a candidate needs 2383 delegates.
Going into West Virginia, Mrs Clinton had 2228 delegates including 523 superdelegates, who are elite party members free to support any candidate.
Mr Sanders had 1454 delegates, including 39 superdelegates.
Another 29 delegates will be apportioned based on West Virginia's results.
- Reuters / BBC