The FBI has issued a fresh warning that terrorists may be interested in using small planes to carry out suicide attacks.

FBI supervisory special agent Steven Berry said Saturday the agency had issued an "intelligence update" to law enforcement regarding small planes but he declined to be more specific.

The Aircraft Owners and Pilots Association said on its Web site the alert was issued because the FBI "has received information indicating that terrorists may still be interested in using small general aviation aircraft for suicide attacks in the United States."

"Pilots are strongly encouraged to remain alert for suspicious activities anytime they are flying, or at an airport just before or after a flight," the association said. "Individuals observing anything suspicious should report it to the local FBI or law enforcement officials."

Andy Cebula, the association's senior vice president for government and technical affairs, said that "while the alert is not specific, it is important that everyone in the general aviation community serve as the eyes and ears for law enforcement, watching suspicious activity and persons."

Berry said the FBI notice was sent to law enforcement officials late in the week. "There's a lot of information that continues to come in from a variety of different sources, and we inform law enforcement or update them, in this case, of any additional information that might be useful in their efforts," he said.

The government has issued a number of alerts about possible threats in the past week, including warnings about possible terrorist activity directed at rail lines, nuclear plants and New York landmarks.