The source, who spoke in New York on condition of anonymity, gave no other details. The FBI in Nevada said only that two men, members of the Aryan Nation, were taken into custody in a luxury car outside a doctor's office in Henderson, Nevada.
Nevada FBI spokesman Aurelio Flores said the car, a white Mercedes, was taken to Nellis Air Force Base for evaluation. Mr Flores said the FBI had secured the area where the car was found and had "made everything safe". He said the agency was not looking for explosives.
Mr Flores said later yesterday that the men arrested in Nevada "were trying to be, maybe, copycats of what happened in Japan".
In Tokyo in 1995, a Japanese doomsday cult was blamed for a nerve gas attack on that's city's subway system. Nineteen people were killed in the subway attack and another nerve gas attack in the central Japanese town of Matsumoto in 1994. The victims died after inhaling or having skin contact with sarin, a poisonous gas.
Referring to the two men arrested yesterday, Mr Flores said: "They might have talked about different cities ... we have no conclusive evidence to indicate that they were talking about a specific city. It was loose talk. The important thing is that everything is safe."
Broadcast reports in Las Vegas and Ohio said one of the two men was Larry Wayne Harris. Last year, Harris, of Lancaster, Ohio, pleaded guilty on a charge of fraud after he was accused of illegally obtaining bubonic plague bacteria through the mail from a laboratory in 1995. He said he never intended to hurt anyone and was sentenced to 18 months' probation. Bubonic plague can be fatal, although it is treatable with antibiotics.
In Washington, a federal law enforcement source said agents were investigating allegations that the two men arrested in Las Vegas possessed anthrax. The source stressed that the tests were not complete and that there have been unfounded instances in the past involving allegations of anthrax. Anthrax is an infectious disease that usually afflicts only animals, but it can be produced in a dry form suitable for weapons and even microscopic quantities can be fatal.
The New York source said the suspects allegedly planned to release a "dangerous bacterial substance" in the subway system, the fifth-busiest in the world.
However, the Mayor of New York City, Rudolph Giuliani, later denied that the city had been targeted. Mr Giuliani, speaking generally about the threat of terrorism, said: "Every part of America, every part of the world, is vulnerable to terrorism ... there is no way to make an open society, a democracy, invulnerable to terrorism or to criminal acts. Short of closing down America and closing down the city of New York, it would be impossible to do that."
The Mayor added: "It is impossible to have a police officer [in] every place. That would be unrealistic, and it would change the nature of a free society. Short of that, I think New York City is doing everything it can do to try to reduce the risk."
Terrorism came to New York in 1993 when Islamic militants bombed the World Trade Center, killing six people and injuring 1,000. Militants also were convicted of planning further bombings at key river crossings and other high-profile targets. US right-wingers were convicted in the 1995 bombing of a federal office building in Oklahoma City, which killed 168 people.
New York City's 722-mile subway system drew 1.13 billion fares last year - surpassing the Paris Metro to become the fifth-busiest underground railway in the world.
- New York (AP)