Washington (CNN) -- Lone individuals are the most likely to launch attacks in the United States following the death of al Qaeda leader Osama bin Laden, according to a joint Department of Homeland Security/FBI bulletin sent to state and local law enforcement.
The advisory says lone offenders who share al Qaeda's ideology are the greatest near-term threat because they are "unburdened by organizational constraints that can slow operational decisions by established terrorist groups."
Individuals could try to attack low-security targets using simple improvised explosive devices or small arms, the message said. However, the May 9 advisory obtained by CNN notes that federal law enforcement officials have "no credible information to suggest that a specifically targeted plot is underway."
The document cited the vow in the al Qaeda statement confirming the death of bin Laden which said "the soldiers of Islam" would continue to plan attacks. The advisory also says over the past year, Inspire magazine -- published in English by al Qaeda in the Arabian Peninsula -- and various jihadi spokesmen have said attacks by individuals "can have a significant impact."
The notice mentions several attacks involving a single perpetrator, including the November 2009 Fort Hood attack that left 13 people dead. Army Major Nidal Hasan is accused in that shooting.
Law enforcement officials have repeatedly warned that plots by lone wolves are the most difficult to detect and disrupt. But the DHS/FBI bulletin urges state and local law enforcement officials to be on the lookout for suspicious activity.