WASHINGTON (Reuters) -- The FBI has collected information about tactics and training used by anti-war protesters in an effort to blunt potential violence by extremist elements, a federal law enforcement official said Sunday.

The FBI warned of tactics used by such groups in a weekly bulletin circulated to 15,000 law enforcement agencies around the country last month before large demonstrations in Washington and San Francisco to protest the Iraq war.

The bulletin discussed tactics, training and organization of groups, some of which have Web sites that refer to training camps to teach activities like disrupting traffic and law enforcement during large public events, the official said.

It described activist strategies like videotaping arrests to intimidate police and using the Internet to recruit and raise funds.

The memorandum was first reported by The New York Times in its Sunday editions, and the contents were confirmed to Reuters by a federal law enforcement official.

"It contains information that we gleaned through investigation and through other means," the official said.

"In the experiences that law enforcement agencies have had in other cities such as Seattle, Washington D.C., San Francisco, where there have been large scale protests, where there was a potential for violent activity, that information was then passed on ... to law enforcement agencies for future planning," the official said.

Sen. Edward Kennedy, a Massachusetts Democrat, said he was concerned about reports that the FBI was monitoring anti-war protesters.

"We have the stories going on this morning where they're using the FBI to look into demonstrations in order to find out who is demonstrating and getting into their background. That reminds me to the old Nixon times and the enemies list," he said on ABC's "This Week." White House officials in the administration of former President Richard Nixon kept a list of political enemies.

Kennedy said the Bush administration had gone to "extraordinary lengths" to attack lawmakers who question the White House policy on Iraq and that was a "fundamental flaw" of the administration. "How could we be fighting abroad to defend our freedoms and diminishing those freedoms here at home?"

The federal law enforcement official said the FBI was only interested in individuals and groups who plotted violence.

"Our interest is not in individuals or groups expressing their constitutional right to protest. It is only those individuals or groups that would be involved in either conspiring, or actively involved in violent or criminal activity in support of a particular cause," the official said.

Civil rights groups and legal scholars quoted by The New York Times expressed concern that monitoring protesters could signal a return to the abuses of the 1960s and 1970s, when J. Edgar Hoover was FBI director and agents routinely spied on political protesters including Dr. Martin Luther King Jr.

The resulting restrictions on FBI investigations of political activities were relaxed last year when Attorney General John Ashcroft, citing the September 11, 2001 attacks, issued guidelines giving agents authority to attend political rallies, mosques and any other public events.