Washington ? The FBI warned Thursday that al-Qaida is likely to attempt a “spectacular” attack intended to inflict large-scale casualties and damage the U.S. economy.

The latest FBI warning was circulated to law enforcement officials nationwide despite a lack of specific credible evidence. It has not led the Bush administration to raise the terrorist threat level above code yellow, or “elevated,” which is the middle of a five-point scale of risk developed after the Sept. 11, 2001, attacks.

“Sources suggest al-Qaida may favor spectacular attacks that meet several criteria: High symbolic value, mass casualties, severe damage to the U.S. economy, and maximum psychological trauma,” says the alert, which was posted on the FBI’s Web site.