GREENVILLE, US - DEMOCRATS Barack Obama and Hillary Clinton renewed their battle over gas tax relief on Monday in a late push for support on the eve of critical presidential showdowns in North Carolina and Indiana.

The candidates, embroiled in a gruelling nominating struggle that has split the party, wooed working-class voters and launched new television advertisements attacking each other ahead of Tuesday's votes.

Mrs Clinton hit Mr Obama for opposing her proposal to lift the federal gasoline tax for the summer, which he says is political pandering. She launched a television ad in both states accusing Mr Obama of attacking her plan 'because he doesn't have one'. Mrs Clinton says her support for a summer-long suspension of the gasoline tax would help Americans struggling with record gas prices in a faltering economy.

Mr Obama, an Illinois senator, responded with his own advertisement saying Mrs Clinton offered 'more of the same old negative politics'. He said the gas tax holiday was a dishonest approach to a real problem.

'There is not a single economist or editorial that I've read that says that this is a good idea, and the reason is, is because it's not being honest with the American people,' Mr Obama said on NBC's Today show. 'People don't need symbolic relief, they need real relief.'

Indiana and North Carolina, with a combined 187 delegates to the August nominating convention at stake, are the biggest prizes remaining in the state-by-state Democratic race. There will then be only six contests left.

Mr Obama leads Mrs Clinton in the race for the 2,025 delegates needed to win the nomination to face Republican John McCain in November's presidential election.

Voting in the Tuesday elections ends in Indiana at 7 pm EDT (7am Singapore time) and in North Carolina at 7.30pm EDT (7.30am Singapore time), with results expected soon after.

State-by-state battle
Wins for Mr Obama in both states would effectively end Mrs Clinton's chances of overtaking him in either delegates or popular votes cast in the state-by-state battle.

But a sweep of the two states by Mrs Clinton would fan doubts about Mr Obama's electability and prolong a rough patch where he has been on the defensive over a big loss in Pennsylvania, his relationship with his controversial former pastor the Reverend Jeremiah Wright and other issues.

Mr Obama told supporters in Durham, North Carolina, his recent troubles 'basically exhaust my problems' and he had moved on.

He attributed the difficulties to his position as the front-runner in the race.

'Senator Clinton, despite what she says about being vetted, she hasn't gone through what I've been going through over the last couple of months because she's not the front-runner,' he said.

Mr Obama leads in polls in North Carolina, although his once double-digit advantage over Mrs Clinton has shrunk to single digits. The two are running close in Indiana, where most polls show Mrs Clinton with a slight lead.

Neither candidate will win enough delegates before the voting ends on June 3 to clinch the nomination, leaving the decision to nearly 800 superdelegates - elected officials and party insiders - who are free to back any candidate.

A split decision on Tuesday would leave the race largely unchanged, with the candidates trying to convince superdelegates they would be the best Democrat to take on Mr McCain.

Mr McCain, speaking to reporters in Phoenix, launched a Spanish language website to mark the Mexican Cinco de Mayo festival on Monday and said Republicans could win back the support of Hispanics.

Hispanics, a fast-growing voting bloc in many battleground states, have moved away from Republicans in the last year after a bruising battle over immigration and the treatment of illegal aliens.

Mr McCain lost some conservative support during the immigration debate by backing a path to citizenship for some of the country's 12 million illegal immigrants. He later said Congress should focus on border security first.

'I believe that the majority of Hispanics share our view that the border must be secured and must be secured first,' the Arizona senator said.

'But they also want us to have an attitude, which I think most Americans do, that these are God's children and they must be taken care of, that the issue must be addressed in a humane and compassionate fashion.' -- REUTERS