(CNN) -- Federal prosecutors charged two men with plotting a "killing spree" against African-Americans that would have been capped with an attempt to kill Sen. Barack Obama while they wore white tuxedos, federal officials said Monday.

Paul Schlesselman, left, and Daniel Cowart said they planned to kill more than 100 African-Americans.

The U.S. attorney's office in Jackson, Tennessee, said Daniel Cowart, 20, and Paul Schlesselman, 18, were self-described white supremacists who met online through a mutual friend.

Both men have been charged with illegal possession of a sawed-off shotgun, conspiracy to rob a federally licensed gun dealer and making threats against a presidential candidate.

The men planned to kill more than 100 African-Americans, including 14 who would be beheaded, according to the affidavit. But federal law enforcement sources said there was no evidence Cowart, of Bells, Tennessee, and Schlesselman, of West Helena, Arkansas, had any details of Obama's schedule.

"We take this very, very seriously but we see no evidence these guys have the ability or the wherewithal to pull off what they say they wanted to do," one law enforcement source said.

According to an affidavit from the federal agent who questioned them, Cowart and Schlesselman planned to charge at Obama with a car, firing from the windows as they went. They would be dressed in white tuxedos and top hats during the attempt, the affidavit states.

Cowart and Schlesselman were arrested outside Jackson, about 75 miles east of Memphis, Tennessee, after an aborted robbery attempt last week, according to court records.

Though they told investigators they would be willing to die in their mission, the men backed out of their October 21 attempt to rob the gun dealer after spotting two cars and a dog at the home, the affidavit states. The men also shot out the window of a church on their way back to Cowart's grandfather's home, where they were arrested the next day.

Cowart and Schlesselman made their initial appearances before a federal judge Monday and are scheduled for a bond hearing Thursday in Memphis.

Obama, an Illinois Democrat, is the first African-American nominee to lead a major-party ticket and was placed under Secret Service protection in May 2007, far earlier than other candidates.

Eric Zahren, a spokesman for the Secret Service, said it was unclear whether the suspects would have had the capability or means to carry out any sort of plot. But he said the matter was being taken seriously, and a joint investigation was under way.

There was no indication either had attended any Obama event or had drawn Secret Service attention in the past, Zahren said.

Campaign spokeswoman Linda Douglass said, "We never comment on security matters."

Threats against Obama have led to arrests in two previous cases. In one, federal prosecutors concluded that the three people arrested with drugs and weapons in a suburban Denver motel posed a "true threat" to the candidate.

In the second, a Florida man was charged with threatening bodily harm against the candidate in August. He has pleaded not guilty.

CNN Chief National Correspondent John King contributed to this report.

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