A feared white supremacist plot to assassinate Barack Obama was dismissed by police last night, who said the three male suspects only face gun charges.

One of four people arrested near Denver was reportedly found with two rifles, ammunition, a telescopic sight, body armour, walkie-talkies and suspected drugs.

One news channel quoted police saying the men, one of whom is alleged to have strong ties to a white supremacist gang, had admitted to a "crude" plan to use a rifle to kill Obama.

However, after hours of questioning officers concluded there was no credible plot to kill the Democratic presidential candidate.

One early suggestion was that Mr Obama was to be targeted by a sniper as he gave his open air address in the Denver Broncos' stadium tomorrow night.

But a police spokesman said the three men and a woman, a girlfriend of one of them, arrested on Sunday were not expected to be charged with making threatening statements, conspiracy or other national security-related crimes. It is possible but unlikely, however, that additional charges could be brought later.

Another police source added: "The capability and their opportunity and what they had for their weaponry - I don't see that they would have been able to carry it out." A news conference about the arrests was due to held last night.

Troy Eid, the US Attorney General, said: "We're absolutely confident there is no credible threat to the candidate, the Democratic National Convention or the people of Colorado.

One of the men arrested told the local television station in a rambling interview that others involved in the case had made racist statements regarding Mr Obama and had discussed killing him on the day of his keynote speech.

When asked if he felt there was a plot to kill Mr Obama, Nathan Johnson said: "Looking back at it, I don't want to say yes, but I don't want to say no."

Johnson was interviewed while being held in jail on drug charges. He insisted he was not involved in any plot.

Mr Obama will become the first black presidential nominee of a major US political party when he accepts the Democratic nomination in Denver, Colorado, tomorrow night.

Events unfolded early on Sunday when a van was pulled over by the police for being driven erratically.

The driver had a suspended driving licence. Inside the van officers found the guns and ammunition. Subsequently, the other suspects were arrested.

The incident follows one at the weekend when a Wyoming hunter en route to a South African safari accidentally caused a security scare at a plush Denver hotel when he entered it carrying two rifles and two guns.

Police evacuated Nancy Pelosi, Speaker of the House of Representatives, after arresting the man.

He later apologised for the disruption he had caused, saying he was unaware that the Democratic National Convention was in town.