A top official of the leading U.S. law enforcement agency says al-Qaida's September 11, 2001 terror attacks in the United States initiated what he calls "a very high tempo of terrorist activity" that continues today. VOA's Stephanie Ho reports from Washington.

FBI Assistant Director John Miller told ABC's This Week program he believes al- Qaida operates on two tracks - planning its own activities and encouraging unrelated groups to strike out against targets in the United States and other western countries.

"I think that al-Qaida is working on a split plan, which is [that] al-Qaida continues everyday to plan the larger, spectacular attacks, something along the lines of a 9/11 or as close as they can get," said John Miller. "At the same time, they pump out an awful lot of propaganda aimed at getting those who think they have the wherewithal to act on their own, to do that."

Miller pointed to a thwarted plot to explode fuel tanks and a pipeline at New York's JFK International Airport as the most recent example of a plot not connected with al-Qaida but inspired by it. The terror plan was revealed Saturday, more than a year after U.S. authorities began their investigation.

Miller said al-Qaida's expanded influence is prompting U.S. authorities to be more vigilant and pay greater attention to groups that probably would have, before al-Qaida, been ignored.

"When you're looking at inspired through the Internet, home-grown extremists, well they can pop up anywhere," he said. "So, now, instead of having a focus in a certain direction, you have to focus in a 360-degree radius, every moment of every day."

Miller pointed to another plot that failed - a plan to bomb airplanes in London that was uncovered last year - as an example of what he called the "latent fingerprint of al-Qaida control." This comment came in another interview, broadcast Sunday by the public affairs cable channel C-Span. Miller added that U.S. authorities, in addition to looking for plots by al-Qaida copycats, remains on the lookout for large-scale operations by al-Qaida itself.

"Now it's been more than five years since September 11, and we haven't seen a successful al-Qaida-driven major attack," said Miller. "But that doesn't mean that we haven't seen them in the works, or seen them taken apart."

Miller refused to state flatly that there are any al-Qaida sleeper cells in the United States. But he hinted strongly that the FBI believes there are. He did say that U.S. law enforcement officials are constantly increasing their surveillance of people they believe to be terrorists or spies.