DENVER— Three men who authorities initially feared were plotting to assassinate Barack Obama at the Democratic National Convention are facing only gun charges — signaling they never posed a real threat.

A federal law enforcement official in Denver said the three men and a woman also arrested on Sunday are not expected to be charged with making threatening statements, conspiracy or other national security-related crimes.

It's possible — but unlikely — that additional charges could come later, the official said, speaking on condition of anonymity because the charges have not yet been filed.

One of the men was arrested near Denver with two rifles, ammunition, walkie-talkies and suspected drugs. Federal officials say two other men and a woman were apprehended a few hours later.

A news conference to discuss the charges is expected at 6 p.m. EDT Tuesday.

The likelihood of an assassination attempt on Democratic presidential candidate Obama was downplayed by law enforcement officials in Colorado and Washington.

"We're absolutely confident there is no credible threat to the candidate, the Democratic National Convention, or the people of Colorado," U.S. Attorney Troy Eid said in a statement.

One of the men arrested told KCNC-TV, the CBS affiliate in Denver, that others involved in the case had made racist statements regarding Obama and had discussed killing Obama on the day of the speech.

When asked if he felt there was a plot to kill 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 said he wasn't involved in any plot.

Three senior FBI officials said it's unclear whether any of the suspects were serious about carrying out threats. The officials spoke on condition of anonymity because they were not authorized to discuss the case.

A fourth federal official familiar with the investigation said an assassination attempt was unlikely.

"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," the official said on condition of anonymity because the investigation is ongoing.

The first arrest came after police in Aurora, a suburb east of Denver, stopped a truck that was swerving erratically around 1:30 a.m. Sunday. The driver, 28-year-old Tharin Gartrell, had a suspended driver's license, and the truck was rented in the name of another person, said Aurora police Detective Marcus Dudley.

In the truck, officers found two rifles, including one with a scope; a bulletproof vest; boxes of ammunition; walkie-talkies; and suspected narcotics. On edge because of heightened security surrounding the Democratic convention in Denver, Aurora police alerted federal authorities.

Later Sunday, federal agents arrested Johnson, 32, at a hotel in Denver. He was held on drug charges. A half-hour later, 33-year-old Shawn Robert Adolf jumped from a sixth-story window when authorities tried to arrest him at a hotel in suburban Glendale, police said.

Adolf was hospitalized and was being held in lieu of $1 million bond for several outstanding warrants involving drug charges. He had a handcuff key in one hand and a swastika ring on the other when he was arrested, a senior FBI official said.

Dudley said Gartrell was being investigated for methamphetamine and firearms violations. Gartrell, who has no known address, was being held at the Arapahoe County jail on $50,000 bail on drug and weapons charges. The jail said he was due in court Thursday.

Gartrell was charged with misdemeanor domestic violence in 2005, but those charges were later dismissed, according to Colorado court records.

Johnson's bail was set at $10,000 on Tuesday; it was not immediately posted. Johnson did not speak during a brief court appearance Tuesday, and jail officials said he was refusing other interview requests.

Also arrested was a woman described by federal authorities as the girlfriend of one of the men. They had no information on what charges she might face.

Law enforcement officials were also investigating whether the men were linked to vandalism shootings that targeted at least two federal buildings in Denver over the past two weeks. Windows were shot at the U.S. Custom House and the U.S. Military Entrance Processing Station on the same street in Denver's downtown Federal District.

Additionally, a bullet was recovered from a Hertz rental car that was hit on Aug. 15, and authorities are now looking to see if it could have matched the guns seized from the men.