Hillary Clinton declared today that she will "never give up" in her battle against Barack Obama after a landslide victory in West Virginia's primary which nevertheless failed to loosen his stranglehold on the Democratic nomination.

Mrs Clinton's huge victory in one of the whitest and most rural states in America nevertheless increased concerns about Mr Obama's ability to win over working class swing voters, after yet another contest in which lower-income white voters defiantly turned their backs on him.

Despite an almost impossible task before her to win the nomination, Mrs Clinton immediately exploited those doubts. She said she would take the battle against Mr Obama all the way to the final contests on June 3. "I am even more determined than ever to carry on this campaign until everyone has had a chance to make their voices heard," she said.

She added, in a message to super-delegates: "Tonight, in the light of this overwhelming victory in West Virginia... to everybody still making up their minds, I am in this race because I believe I am the strongest candidate to lead our party in 2008 and the strongest president to lead our nation starting in 2009."

She added, to a cheering crowd in Charleston: "You will never be counted out, and I won't either. You will not quit, and I won't either."

Yet Mrs Clinton also praised Mr Obama and indicated how tough her battle is: "I will work my heart out for the nominee of the Democratic Party to make sure we have a Democratic president." She said that a shared "commitment to bring America new leadership means we have always stood together on the most important issues".

Today, Mrs Clinton is due to appear on most evening news programmes and later in the week will campaign in South Dakota - a state that votes on June 3, the final day of the nominating calendar.

Even before Mrs Clinton's widely predicted victory, Mr Obama alluded to concerns about his difficulties in attracting lower-income voters in a speech in Macomb County, Missouri, an area dominated by so-called Reagan Democrats. Early indications were that he lost West Virginia by a margin of two-to-one.

Referring to growing scrutiny over the way blue-collar households view him and worries among Democrats that his battle against Mrs Clinton has split the party along race, gender and class lines, Mr Obama said: "There is a lot of talk these days about how the Democratic Party is divided. But I’m not worried, because I know that we’ll be able to come together quickly behind a common purpose. There’s too much that unites us as Democrats."

His visit to Michigan was the start of a sweep through states that have already had Democratic primaries, but are marked out by Mr Obama's aides as battlegrounds for the general election in November against John McCain, the Republican nominee-elect. He spent the rest of his address focused on the Arizona senator - who according to polls is very competitive - declaring: "John McCain is running for four more years of the same approach that has failed the American people."

Today Mrs Clinton is expected to meet her big donors and advisers for a meeting about the future of her presidential bid.

Mr Obama has an almost insurmountable lead among elected delegates and since his 14-point win in North Carolina last week has won 27 super-delegates. The mathematics is overwhelmingly against Mrs Clinton. To win the nomination, she would have to win each of the five remaining contests with at least 80 per cent of the vote and take a similar portion of uncommitted super-delegates.

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