Hillary Clinton has beaten Barack Obama in West Virginia's Democratic presidential primary by a large margin, US media outlets have projected.
Senator Clinton held a big opinion poll lead over Mr Obama ahead of the vote.
Mr Obama remains the clear frontrunner in the overall contest to become the party's nominee, having garnered more support and cash.
Correspondents say even a big Clinton win in West Virginia will do little to alter the race.
In the primaries and caucuses so far, Mr Obama has won more of the delegates who will choose the party's nominee at the Democratic National Convention this summer.
An additional two dozen super-delegates - party and elected officials - have declared their support for him in the past week, according to the Associated Press news agency, swelling his lead.
Pressure
In an email to her supporters, Mrs Clinton made it clear that she had no intention of dropping out of the race.
"It's clear that the pundits declaring this race over have it all wrong," she wrote.
"The voters in West Virginia spoke loud and clear - they want this contest to go on... I'm going to carry the energy of tonight's victory into the next contests in Kentucky and Oregon."
Mrs Clinton campaigned hard in West Virginia, although only 28 delegates were at stake.
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Voters in West Virginia's Democratic primary make their choice between Hillary Clinton and Barack Obama
She hopes this big win will bolster her argument that she is stronger than Mr Obama in the kind of states likely to be key battlegrounds in November's general election, analysts say.
The state's demographics were in her favour, with a population that is 95% white, largely blue collar and culturally conservative, groups which have tended to support Mrs Clinton in previous primary elections.
Exit polls indicated that Mrs Clinton maintained her strength with these groups in West Virginia.
White voters without college degrees - who made up two-thirds of the electorate - backed Mrs Clinton three to one, according to surveys conducted by the AP news agency.
West Virginians' attitudes to race may also have helped Mrs Clinton, the surveys suggested.
Of the 20% of voters who said that race had influenced their choice (one of the highest proportions so far during the primaries), 80% supported the New York senator.
She also led Mr Obama among groups who have tended to back him in previous contests, including voters under 30, college graduates and independents.
US TV networks were able to call the race for Mrs Clinton as soon as the polls closed at 1930 local time (2330 GMT).
Mrs Clinton has resisted pressure to bow out of the race, despite Mr Obama's growing advantage in terms of delegates and her rapidly dwindling campaign war chest.
Campaigning on Monday, she said: "I wouldn't be doing this if I didn't believe that I could be the best president for West Virginia and America and that I was the stronger candidate to take on John McCain in the fall."
After West Virginia, only a handful of primary contests remain before the Democratic Party officially declares at its August convention who will take on presumptive Republican candidate John McCain in November.
The next primaries will be in Oregon and Kentucky on 20 May.
Shift of focus
Mr Obama appeared in Charleston, West Virginia, on Monday but appears to have largely switched his focus to a potential general election campaign against Mr McCain.
Hillary Clinton is trailing rival Barack Obama in the overall Democratic race
His only public appearance on the evening of the West Virginia result was in Missouri, a state that has already held its Democratic primary, but which will be a key battleground in the general election this November.
Speaking at a factory in the state, Mr Obama made no reference to the West Virginia contest, and focused almost all of his remarks on Mr McCain.
In the coming days he will also visit Michigan and Florida - both expected to be general election battleground states - as well as remaining primary states South Dakota and Oregon, his campaign said.
In Nebraska, both parties are holding primary elections to choose their nominee to compete in November for the Senate seat of retiring two-term Republican Chuck Hagel.
A Republican presidential primary is also taking place, although Mr McCain is already the effective nominee.
Nebraska's Democrats held their presidential caucus on 9 February.
Congressional contests are also taking place in West Virginia and Mississippi.
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