Problems with electronic voting machines and allegations of ballot rigging and intimidation triggered a flurry of dirty tricks accusations from both sides today.

The protests were loudest in the most closely contested states and mostly from Democrats, many of whom are convinced that the last two presidential elections were stolen from them.

The FBI said that it was investigating complaints that voters in Virginia had received telephone calls with misleading information about where their nearest polling station was located.

The bogus calls included some from people claiming to work for Jim Webb, the Democratic senatorial candidate, fuelling suspicions among Democrats of Republican chicanery in a Senate race crucial to who will control the chamber.

Although there was no hard evidence of Republican dirty tricks, Democrat suspicions have been bolstered by a revelations about the reliability of the machines and the political affiliations of the companies that own them.

Since the 2000 Florida recount, the US government has spent $3 billion to help states overhaul their voting technology. Over 90 per cent of polls yesterday were equipped with new computerised voting machines.

In 2004, the former head of the biggest provider, Diebolt, wrote a fundraising letter stating that he was committed "to help Ohio deliver its electoral votes to the President".

In Ohio all 12 voting machines in a predominately black district in Cleveland crashed when voting opened at 6.30am, feeding fears that minority and largely Democrat-leaning voters were being disenfranchised.

Election officials in Indiana went to court to get a three hour voting extension after a computer glitch in 70 precincts delayed poll opening.

Colorado Democrats were opposed by the Republicans when they asked a state judge to allow late voting, arguing that malfunctions had forced long queues to wait up to two hours while others were turned away.

In Maryland, Democrat officials accused Republicans of launching a campaign of voter intimidation after it emerged that the party's poll watchers had been issued with a handbook urging them to challenge voters who they suspected of not being registered to vote.

Democrats said the tactic was reminiscent of intimidation used against blacks during the Civil Rights era.

In Florida’s Broward County, notorious for the "hanging chad" debacle in the disputed 2000 presidential race, 14 voting machines in one precinct stopped working for 90 minutes.

But in New Jersey it was the Republicans claiming to be victims of a dirty tricks operation with their candidate, Tom Kean, alleging that his campaign headquarters had been padlocked by Democrat operatives. His opponent claimed it was a Republican stunt.

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