He told KDKA, a Pennsylvania station: "I think what's been striking about this campaign is the degree to which these kind of hate groups have been marginalised. That's not who America is. That's not what our future is."

'Amateurish' plot

Cowart and Schlesselman have been charged with possessing an unregistered firearm, conspiring to steal firearms from a federally licenced gun-dealer and threatening a candidate for president, the AP news agency reported.

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The men reportedly planned to kill 88 people - 14 of them by beheading - according to documents unsealed in the US district court in Jackson, Tennessee, on Monday.

The men then allegedly planned to drive a car at high speed towards Obama, while wearing white tuxedos and top hats, and shoot him, authorities said.

The numbers 88 and 14 are symbolic in the white supremacist community.

A picture obtained by US media from Cowart's MySpace page shows him holding what appears to be a weapon.

However Eric Zahren, a spokesman for the US Secret Service, told AP that "whether or not they had the capability or the wherewithal to carry out an attack remains to be seen".

Court documents said the plot appeared amateurish, Reuters reported.

Target fears

US police also said there was no evidence so far that others were willing to help Cowart and Schlesselman with the plot.

Obama, the first black presidential nominee of a major political party, has had Secret Service protection much earlier in the US presidential campaign than any other presidential candidate because of fears he would be targeted by racists.

In August, three men were arrested, reportedly with a weapons cache, in Denver, Colorado, where the Democratic Party convention was being held.

However, the authorities later said there had been no credible threat against Obama.