The FBI has not detected any individuals or cells actively planning attacks such as those almost two years ago that killed some 3,000 people in New York, Washington and Pennsylvania. Most al Qaeda operatives in the United States provide logistical support such as travel documents, recruitment and fund raising, said Larry Mefford, the FBI's chief counterterrorism official.
"My view is, it's very small but it does exist," Mefford said of al-Qaeda's U.S. presence. "Our concern continues to be what exists in the United States that we're not aware of."
Separately, a new advisory from the Department of Homeland Security said the agency is "concerned about al Qaeda's continued efforts to plan multiple attacks against the U.S. and U.S. interests overseas."
The advisory, released Thursday, said there was no specific threat at this time, and did not raise the nation's terror alert status from its current yellow or "elevated" level. But it warned that "a growing body of credible evidence" suggested al Qaeda was planning to hijack aircraft flying near or over the United States.
The FBI's latest weekly bulletin to state and local law enforcement agencies cautions terrorists might use two naturally occurring toxins - nicotine and solanine - to poison U.S. food or water supplies.
Nicotine is found in tobacco plants. Solanine - a toxic alkaloid - is found in small amounts in some vegetables, including potatoes that are old or have been exposed to sunlight for a long time. Other plants containing solanine include nightshade, eggplant, and green peppers.
The bulletin, obtained Thursday by The Associated Press, says that terrorist manuals and documents recovered at al Qaeda sites in Afghanistan contain references to use of both substances as poisons.
The FBI said there are no known uses of either toxin by al Qaeda or other Islamic extremist groups, and there is no intelligence indicating such an attack is imminent. But the bulletin noted a Michigan man pleaded guilty in May to lacing 250 pounds of ground beef with an insecticide containing nicotine, sickening 92 people, in an attempt to get a supermarket co-worker in trouble.
Such lone offenders, whether al Qaeda sympathizers or domestic criminals, are a concern to the FBI because they are so difficult to detect. But Mefford said the FBI's main focus is on tracking known al Qaeda operatives in the United States to gather intelligence on their contacts and intentions.
Mefford told reporters that the FBI's strategy is to keep suspected al Qaeda operatives under surveillance for as long as possible and document any criminal or immigration violations they commit. The FBI can then arrest the individuals at a moment's notice to disrupt or prevent terrorist operations from going forward.
"We may develop beneficial intelligence information from watching that group operate, or it may be at a point where we need to disrupt that activity," Mefford said. "That's a judgment call we will make tactically."
The FBI bulletin said there is no intelligence indicating that al Qaeda is planning an attack to coincide with next week's two-year anniversary of the Sept. 11 terror attacks. Al Qaeda, the bulletin said, is not known for using such anniversaries for its attacks, preferring surprise.
Yet Mefford said history is not necessarily a guide.
"They're a very flexible organization," he said. "Clearly, they have the ability to change and adapt to their environment, and that's what we're seeing today - they're evolving."
The FBI's Mefford said al Qaeda remains America's most dangerous terrorist foe because of the group's tenacity, patience and willingness to use tactics, including weapons of mass destruction, that demonstrate "they have no inhibitions and they have no rules."
The Homeland Security advisory says recent arrests may have disrupted al Qaeda, but have not altered its intent to "conduct synchronized attacks against U.S. interests" — against commercial aviation in particular.
"A growing body of credible intelligence indicates al Qaeda continues to develop plans for multiple attacks against targets in the US involving commercial aircraft, with some plans calling for hijacking airliners transiting near or flying over the continental United States — but not destined to land at U.S. airports," the report said.
The advisory said al Qaeda operatives have been looking for countries with porous airport security as bases for attacks, and showed great interest in the government's decision to suspend policies that allowed travelers to transit through the United States without visas.
The advisory also said al Qaeda saw "critical infrastructure" — nuclear plants, railroads, reservoirs — as key targets, and still sought weapons of mass destruction.
In related developments:
"The National Park Service has failed to successfully adapt its mission and priorities to reflect its new security responsibilities and commitment to the enhanced protection of our nation's most treasured monuments and memorials from terrorism," the 24-page report says, according to the newspaper.