Democratic presidential hopeful Barack Obama said he was not worried about threats to his life as he vies to become the first black US president, saying instead that hate group have been marginalised by his candidacy.

"You know, look, 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," Obama told Pennsylvania television station KDKA late on Monday.

"What I've found is that people here, they don't care what colour you are. What they're trying to figure out is who can deliver," he said.

Asked if he was concerned about his safety, Obama said no.

"I've got the best folks in the world — the Secret Service," he said.

On Monday authorities announced the arrest of two white supremacists for threatening to kill Obama during a "killing spree" of some 100 African-Americans.

Daniel Cowart (20), and Paul Schlesselman (18), were arrested Wednesday in Tennessee for possession of firearms, threats against a candidate running for president and conspiring to rob a gun store, the Department of Justice said.

The men began "discussing going on a 'killing spree' that included killing 88 people and beheading 14 African Americans," Brian Weaks, an agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives told a Memphis court on Monday.

"They further stated that their final act of violence would be to attempt to kill/assassinate presidential candidate Barack Obama," he added, as the two men appeared before the federal court.

Cowart, from Bells, Tennessee, and Schlesselman, from Arkansas, met via the Internet a month ago and have "very strong beliefs and views regarding 'White Power' and 'Skinhead' views," Weaks told the court.

Obama, who has made history by becoming the first black presidential nominee of a major political party, is under secret service protection as a candidate. His federal protection began much earlier in the campaign than any other presidential candidate.

In late August, the alarm was also raised when it was revealed three men were arrested with a weapons cache in Denver, Colorado where the party convention was being held. US attorneys later said there had been no credible threat against Obama.

AFP