By Andrew Ward in Washington

Mrs Clinton said she could build a broader support base than Barack Obama, her rival for the Democratic nomination, because of her strength among working-class white voters.

Critics accused her of “race-baiting” for equating white people with hard work and said the remarks would further inflame racial splits within the Democratic party.

In an interview with USA Today, she cited a news report on how Mr Obama’s support among “hard-working Americans, white Americans, is weakening again, and how whites in both states who had not completed college were supporting me”.

Mrs Clinton won 60 per cent of white votes in the North Carolina and Indiana primaries on Tuesday. Mr Obama’s clear win in North Carolina, where almost 40 per cent of Democrats are black, coupled with a narrow loss in Indiana, extended his almost insurmountable lead in the Democratic race.

But Mrs Clinton has vowed to keep fighting at least until the last primary on June 3. All six remaining contests are in heavily white states, including next Tuesday’s in West Virginia.

The Obama campaign said Mrs Clinton’s remarks were “not true and frankly disappointing”, arguing that Mr Obama had performed strongly among white voters in many parts of the country.

Mr Obama’s white support is strongest among the young and college-educated, prompting one Clinton ally to warn this week that Democrats could not rely on “eggheads and African-Americans” to win the White House.

Addressing a rally in West Virginia on Thursday, Mrs Clinton pressed her case that she had the best chance of beating John McCain, the Republican candidate, in November. ”We need to bring back hardworking people to the Democratic Party,” she said. ”I’m winning Catholic voters and Hispanic voters, blue-collar workers and seniors — people Senator McCain will need in the general election.”

Mrs Clinton’s comments sparked fierce criticism from bloggers on liberal websites. One accused her of implying that Obama supporters were “either effete white intellectuals who don’t work, or lazy blacks who also don’t work”.

Her remarks appeared certain to increase concern among senior Democrats about the divisive nature of the contest, amid mounting pressure on her to drop out in the interests of party unity.

More than half of Clinton supporters and about a third of Obama supporters would not vote Democrat in November if their candidate lost the nomination, according to exit polls in Indiana and North Carolina.

Mrs Clinton entered the presidential race with more black support than Mr Obama, stemming from the popularity of former President Bill Clinton among African-Americans. But blacks have grown steadily more enthusiastic about Mr Obama, who would be the first African-American US president, while becoming disillusioned with the Clintons.

The Financial Times