DENVER, Colorado, (AFP) - Four people have been arrested in Denver amid fears of a plot to kill Democratic White House hopeful Barack Obama, a local report said Monday. Denver-based CBS34 said one of the men arrested had told authorities they were "going to shoot Obama from a high vantage point using ... a rifle ... sighted at 750 yards (meters)." The shooting was supposed to happen on Thursday when Obama will accept the nomination as the Democratic Party's presidential candidate for the November elections at the 75,000-seat Invesco stadium, the television station reported. CBS34 also reported that one man was arrested on Sunday after police found two high-powered rifles in a rented pick-up truck he was driving, while another man in custody reportedly was wearing a swastika and was thought to have links to white supremacist groups. The alleged plot was being investigated by the Secret Service, which is in charge of coordinating security for the Democratic Party convention as well as the FBI and the joint terrorism task force. Obama faces "no credible threat" from what had appeared to be a plot on his life, CNN reported Tuesday, citing authorities who nevertheless are pressing on with their investigation. The network reported that office of the United States Attorney said law enforcement officials are "absolutely confident there is no credible threat to the candidate." But CNN reported Tuesday that the suspects had been detained on firearm charges and for possession of the illegal drug methamphetamine, causing authorities to question whether the Illinois senator's life ever had been in danger. The cable network quoted one official as saying that the alleged plot may be nothing more than "some methed up yahoos high on drugs, talking out of their heads." Late Monday, US Attorney Troy Eid told local media he did not believe there was a threat to Obama. "We're aware of the matter discussed tonight by the Aurora Police Department," Eid said in a statement quoted by the Rocky Mountain News daily. "Federal law enforcement is working hand-in-glove with the Aurora Police Department. Because this matter is currently under investigation, there is little we can say right now. "We can say this: We're absolutely confident there is no credible threat to the candidate, the Democratic National Convention, or the people of Colorado." Asked about the alleged plot on Obama's life, campaign spokeswoman Anita Dunn said: "We are not commenting on security issues."