Obama spoke in front of a rally of 100,000 people in St Louis [Reuters] 

John McCain, the Republican presidential nominee, has taken his campaign to the battleground states of North Carolina and Virginia as he attempted to close the gap on Barack Obama, his Democrat rival.

Obama, who spoke at a rally of 100,000 people in Missouri on Saturday, has a four point nationwide lead over McCain, according to a Reuters/C-Span/Zogby tracking poll.

Speaking to supporters at a rally in Concord on Saturday, McCain again attacked Obama over his tax plans and repeatedly referred to Samuel "Joe" Wurzelbacher, a tradesman from Ohio whom the Arizona senator made famous at the third presidential debate.

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"Joe's dream is to own a small business that will create jobs in his community, and the attacks on him are an attack on small businesses all over the country," McCain said.

Since Wurzelbacher was brought up by McCain at the presidential debate on Thursday there has been huge media interest in him, including reports that revealed he does not have a plumber's licence and would actually get a tax cut under Obama's plans.

Earlier in a radio advertisement, McCain said Obama would raise taxes on some people in order to give handouts to others.

"Barack Obama's tax plan would convert the IRS [Internal Revenue Service] into a giant welfare agency, redistributing massive amounts of wealth at the direction of politicians in Washington," he said.

'Out of touch'

Obama, who drew his biggest crowd of the campaign at the Jefferson National Expansion Memorial park in St Louis, dismissed McCain's criticism as misleading.

"John McCain is so out of touch with the struggles you are facing that he must be the first politician in history to call a tax cut for working people 'welfare'," he said.

McCain trails Obama in a number of swing states, according to polls [AFP]

"The only 'welfare' in this campaign is John McCain's plan to give another $200bn in tax cuts to the wealthiest corporations in America."

Under the electoral college system in the US, citizens cast votes for the electors in their states. Candidates need to secure the votes of 270 of these electors to become president.

McCain is currently concentrating on holding battleground states which were won by George Bush, the incumbent president, in 2004, but could now fall to Obama.

The last Democratic candidate to win North Carolina was Jimmy Carter in 1976, when the Republicans were reeling from Richard Nixon's resignation following the Watergate scandal. Virginia has not voted for a Democratic nominee since Lyndon B Johnson's landslide victory in 1964.

In recent polls of battleground states by CNN and Time, Obama leads McCain by five points among registered voters in Colorado, by eight in Florida, by 10 points in Virginia and by three points in Missouri, where the Democratic nominee campaigned on Saturday.

Voter fraud

Meanwhile, Obama's campaign has accused Republicans of using a crusade against voter fraud to suppress legitimate voters.

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Bob Bauer, the senior lawyer for the Democratic campaign accused Republicans on Friday of recklessly "plotting" to suppress legitimate votes and to "sow confusion and harass voters and complicate the process for millions of Americans".

An estimated nine million new voters have registered for the election, and the Obama camp says Democratic registrations are outpacing Republican ones by four to one.

But the McCain campaign says that an untold number of those registration forms are false and warned that illegally cast ballots could alter the results of the election.

On Friday, a supreme court ruling blocked a challenge to as many as 200,000 of the more than 600,000 new registrations submitted in the state of Ohio.

Source: Agencies